Maybe watch for another upper from PK Firearms or BCM that comes with a bcg, then swap the bcg over to your psa upper or just keep the new upper and sell the psa upper if you prefer the new one. It may be a stretch on the budget immediately... but you should have no problem unloading the upper you don't want quickly, sans bcg, and not lose money. I did this (buying a second upper w/ a bcg) and actually traded my original psa upper for a custom handgun (plus he offered an extra hundred), which I will likely sell if my wife doesn't like it.
Other thing, some notification emails are just not being sent out as they can't deal with the load (except midway). Try http://www.arpartsfinder.com/
to watch for a bcg or maybe an upper with a bcg if you can swing what I did.
Anyways, good luck.