Today, with the advent of digitization, many such items are becoming more available through online sources. If not online and available over the Internet, then they might be available within the walls of an institution. One big reason for them not being available is funds—digitizing machines cost over 100,000 dollars for one of decent professional quality, and then there are the staff costs. If some smaller organization wants to use a 50- or 100-dollar desktop scanner to render materials into a digital format that may also work, with the proviso that one can do much more with better equipment. Sometimes copyright or other restrictions have been put on materials; therefore, they can be reformatted but not made available over the web. So, there are a number of reasons why things may exist but not be searchable online. Of course, a lot depends on finances. My own library has a lot of plans to digitize more items in the collection and make them available for researchers. However, we will have to get grants to do this, as funding from the normal budget is slim, indeed.
But a lot of such materials are available and more are coming online everyday. A great advantage of that is that many people (family researchers, teachers, students, historians, and, of course, the general public) can use these materials without doing them harm from overuse or careless handing. From an owner's point of view, this also allows things to be made available and even sold under some set of controls (see https://www.sandiegohistory.org/online_resources.html for an example of how items can be made available, subject to restrictions. While not the be all and end all, digitizing is far better than doing nothing for the collections. Digitizing allows access to fragile items, and storytelling about the history and people of an area.
Following are some examples of these smaller collections that could be useful in your research.
One archive that comes to mind are those items held in the Henrietta, New York Public Library and its local history page. While it is a smaller public library, it contains a selection of materials that deal with the settlement, history, culture, and even genealogy of that area. By the way, it is not far from where Brigham Young of Latter-Day Saints fame lived in Western New York! The library's web site has a summary of what is available in the library itself, but it also has a digital collections page, which links to Journals, Diaries, and Personal Correspondence. With all of this one has easy access to fragile items from the early history of the area (I know, I was there when they were digitized!) One such item is entitled, Journal of James Sperry, a Journey from Henrietta, NY through Ohio, Indiana, and Michigan, beginning October 27, 1835, which covers a lot more than just the town in Monroe County, New York, where James Sperry lived. It is a nice glimpse of times past and how those living at the time perceived them.
Then there are sites such as Halton Hills Public Library in Ontario, Canada. Halton Hills is a town in the Regional Municipality of Halton, west of Toronto, located within the Greater Toronto Area (GTA). It has a web site that allows searching in various kinds of materials. This site allows for the remote use of the 1877 history of that area. Again, because it is available online 7-24-365, someone can use it from wherever in the world they are located, and not have to actually go to the library or archive that holds it, in order to use it. They have also digitized various records from local newspapers. Items can be captured with a screen shot, downloaded as PDF files, and so on. While it's not the same as actually holding an item in your hands, one can use it without having to spend money to get there. But there is also the old standby, microfilm. Recently, Steven W. Myers wrote in the Genealogy Gems newsletter sent out by the famous Allen County (Indiana) Public Libraryabout a 57-reel set of papers dealing with Livingston Manor, in eastern New York State. It was entitled "The Robert R. Livingston Papers, 1658-1888." Many people's families moved from that area to other parts of the country. He discussed what kinds of genealogical materials might be found in them. Fort Wayne, Indiana and Albany New York are more than 500 miles apart. But that's the point I am hoping to make. By looking in many different locations you might find detailed information. Who would have thought that a collection helpful to eastern New York State would be found in Indiana?
The moral of this tale? There are more places to search than a library building, the county courthouse, or (shudder) "the Internet." Archives can be extremely helpful to your research. And there are guides to them. The 62-volume set of Guide to Historical Resources in [name of county], New York, Repositories, is one series with which I am familiar. It was published in print format in the early 1980's in Ithaca, New York, by the New York Historical Resources Center, at Olin Library, Cornell University. It includes a descriptive register of collections and an index. The particular title for my county (Monroe) is cataloged under the following subject heading in our catalog - Archives New York (State) Monroe County.; Monroe County (N.Y.) History Sources. New York (State) History, Local. Other Names - Cornell University. New York Historical Resources Center.
I love what this web site says about such research: "Be aware that records on the same topic, geographic region, family, etc. may be located in several different places. For example, for any one family there may be: naturalization records at a county clerk's office; birth, death, and marriage records at the New York State Department of Health's Bureau of Vital Records; baptism records at the family church; records documenting individual members' educational or employment histories at historical societies; manuscript repositories; or college archives."
So, keep this is mind. Just searching the Internet and even going to your local library isn't enough for good searching. I have been a volunteer at a Family History Center for 25 years, and many times I have had users say, "I checked everywhere and there's nothing," or "I looked at the Internet, and there's nothing useful there." Not true. Archives can contain physical descriptions of people, causes of death, and places of marriage, not to mention explicitly stating relationships. To close, I will mention that the University of Rochester archives has a lot of family papers from the Rochester family, and in these were found previously unknown facts about the founder of my city. In fact, my library holds his actual will in our archives. You might well find such things if you arrange and archival assignation.