I wrote back in October how NPD was planning to offer parts for Pontiac GTOs. I have an update from Derek Putnam, Project Manager for GM Car Catalogs for National Parts Depot:

We’re still adding new products to our arsenal before we release the GTO/Lemans/Tempest catalog. At this point we’re looking at a June 2012 publish date. If you are looking for anything in particular at this point, we already have about 2000 part numbers in stock, so feel free to ask!

So it seems that you can order GTO parts from them. Just give them a call and tell them what you need. I'll provide a more comprehensive review of my customer experience and of their GTO parts catalog next month.

National Parts Depot