Lots of good, used parts here:
Frank's Pontiac Parts
I have purchased lots of parts for many Pontiacs from AMES Performance http://amesperformance.com/
and Inline Tube (ask for their Pontiac catalog) http://www.inlinetube.com/
You can also find a lot of Pontiac parts at Performance Years, Year One and NPD...and don't forget to check Rock Auto. I was surprised at how many classic parts they carry.
I also have found that patch panels and replacement sheet metal from Dynacorn, Sherman Associates and other suppliers is often available through a local Auto Value, NAPA or Auto Zone store. You can usually get the parts at the local store without paying shipping costs.
Welcome to Pontiacs!