Nvm, I found it!
https://faforever.github.io/db/relationships.html
Hopefully, this is up to date.
Not sure I can do a table join in the client. I need to figure out how to run an arbitrary query so I can play around with it.
For the OP's problem, searching for high-rated players is about the best you can really do.
There probably are not many 4v4 games where everyone is 2000+. There just aren't many players at that level.