I found a new source for Pontiac GTO parts (and other brands, including Buick, Chevy, Ford, Mopar and Oldsmobile). It is Inline Tube, a company that specializes in "a variety of products for all classic cars and trucks... preformed brake lines, fuel & transmission lines, and straight length tubing sets, for custom applications and the street rod enthusiast... stainless and OEM parking brake cables, brake and fuel line clips, stainless and OEM brake flex hoses, proportioning valves, disc brake conversions, rear drum kits and many other under body products".

I've yet to buy anything from them but they came up in a Google search I was doing for a gas tank filler neck for my 1968 GTO (something that is impossible to find, unless it comes off a doner car, in which case it is mildly impossible to find - side note: looks like the Parts Place is the only one that offers this - a new tank for a 68 that comes with the filler neck).