Can't seem to find a ready to install gasket for the AC condenser box. Can these be bought or is something else being used?

Thanks in advance.

Just went through this myself, and BTW I think you're refereing to the evaporator box (condenser is in front of radiator). To my knowledge there were 2 types of gaskets. 1. A square gasket that seals the left side of the evaporator (standing in front of your car). 2. Two of the same gaskets that mount on the outer edge on the evaporator. The box halves are sealed with monkey [censored] (strip caulk) and so in the firewall side. I used HVAC tape for the 2 edge gaskets, the square one is still available. The are the same for most GMs when you google it.
http://thefirstgensite.com/library/partscounter/illustrated/heatair/air1.html

Thanks for the info ramair68.