Where did you purchase the ass pad?

Revzilla.  It's an AirHawk2.  If I were to do it over, I'd spend the extra dough on the original AirHawk.  The AirHawk2 has literally saved my ass.  The original uses a neoprene bladder instead of a non-flexing one.  I'll bet the neoprene is even more comfortable.

In fact, I think I'll order that today.