One long-term solution would be to ask the relevant question in a relevant community on lemmy every time this happens to you. Then answer it yourself (or wait for other to), perhaps using the other site (via archive.org) as a reference when writing it up.

The important bit is to make sure the answer here is complete and not just a link to outside sources. That way it won't disappear if those other sites go offline.

With enough people doing this we can push lemmy into those search results and build a useful & independent repository of knowledge.