He gets them from whoever the fuck sells to him, that's where.
Show me one time we do 'prove it or your guilty,' if there's no proof why would we ban someone? Chat logs =! proof. That's to protect your 'innocent until proven guilty' thing. Otherwise, barely any proof would be needed.
If you're trying to make that in to Dorians ban, apparently, Sin caught him trying to buy ********s with the same MSN. So, he was technically, proven guilty.