I think you would need a database of products, mainly programs, that contain software solutions. I suppose lists can be found in things like old freeware and shareware catalogs, commercial catalogs and so on. If possible a short description of the product should be included. And a list of versions with the date they where released. Perhaps there need to be also a catalog of methods or solutions with some structure in it that can be linked to products. In an ideal world the used software technics for each product would be documented so that they can be searched. Then I think it all depends on who is inputting the data and if the source code can be accessed. Patents can claim methods that should be found in the source but more likely things that have to do with the look and feel for the user of a product and that would not be obious looking at the source.
Perhaps the authors of some older free software would be willing to input a description of their product as a way of protecting their ideas.
Others with access to the code (open source or code that has been released in one way or an other) could also make a description of the used methods. Perhaps a tool can be developed to find some methods in a database of source code and/or comments found in source code.
For products with no available source code it is perhaps possible to put the manual in a database (if there are no copyright objections). Searches in the manuals may direct people in the correct direction. Still, lots of work would have to be done, like running the old product on emulated old system, to be sure that it is prior art.
A database of users manuals looks to me as the most promising approach. Together with the short description of the products.