They already have an affiliate program:

https://swcpoker.eu/affiliates/

It's actually pretty generous if you have a good network of contacts to refer.

The old sealswithclubs often had between 300-500 players online in the final months, which is a respectable figure in my opinion.  It was enough that you could find action at basically any stakes at almost any time.  That's not something that I've found elsewhere, but then again, a lot of the other provides ask you for dox or they don't run on linux or some other stumbling-block.  Nowadays swc is without it's non-windows people.  I think once they straighten that out they'll see their numbers basically double from what you're seeing now.