No help here but funny story. Years ago I had been in a similar situation trying to get in at demonoid and was so frustrated. One night at the bar I was bitching about it to my wife and some dude randomly overheard and says hey bro I've got an invite I'll send you one now if you want. That was a good night. Long story short, go to a bar and whine about it loudly, you never know!

1. Find a tracker with open invites or a recruiting interview
2. Be a positive part of that community, seeding forever, and becoming (usually) Power User or higher
3. Look through the invites available in the PU+ forum section for other communities that interest you, and get invited from there