I discovered BetaArchive today and got so excited, as I had just found another seemingly incredibly easy to find archived software, until I learned you first need to contribute something in order to have access to the files.
In my opinion, that's fucking stupid. You need to have an unreleased, lost, or otherwise not already archived piece of media (heavily unlikely) and the tools to get them in a state that you can upload it (which, depending on the type of media, can wildly vary). The chances of you actually having something to upload and be accepted are very low.
Honestly, just upload to the Internet Archive.