Nopes, haven't bought PSN codes from anyone other than amaga, although I have been told by people that they have bought $50 codes from him for 4K, and from Devilwing for as low as 3.5K.
But like amaga pointed out, it is a bit risky. If either of those two people use hacked credit cards to acquire these codes, it could lead to a perma-banned PSN account.