That particular Giant Eagle (or Gi'nt Iggle, as a native might say) is one of the "special" Giant Eagles in the area - it's one of the biggest supermarkets you'll ever see, and it carries everything. They always have Pat Transit passes. Make sure, if you buy one, that you a) buy the weekly pass, and not the book of tickets, and b) you buy a two zone pass. Bethel Park is two zones away from downtown (or dahn tahn, as a yinzer might put it).
The store, btw, is 24 hours, but Customer Service, where you get that pass, closes down around 10pm.
Wow, man. Talking about Giant Eagle on the DISboards.
Oh, it's on Oxford Drive. You might be able to walk around behind the parking lot to get there. If you can't, go out the front, turn left on Fort Couch Road, and turn left again on Oxford Drive. You can't miss it.