Sorry for the cross post/repost, I put this in racing as well but its very necessary
Racing underground is open for registrations without invites for a very short time. I think there is a count down and we're talking mere hours remain.
-- EDIT --
Registration closed today at 11. Most people cannot give out invites as it takes both seed time and posts to get in with the community before invites are made available, sorry. For the record, I'm not affiliated with these guys at all so I can't hand them out either.