You can't complain too much, as this same thing has held true throughout the history of classic cars. No more than you or I could reproduce the parts easily, the aftermarket isn't going to produce many parts for the less popular collector cars because they can't do all the tooling and machining at a profit.
You can find just about any part for a 60's Mustang reproduced new. Obviously the same wouldn't hold true for a '70's Maverick. Why? The Mav ain't nearly as popular. That is why with the G bodies you see most of the aftermarket stuff available is for Chevy 2 door Malibus, Montes, and Elcos because they are the most popular of the G's that people restore. The dozens of other makes, models and styles of G's are far less popular.
The rule that applies here is if you want to have a nice less popular model of a car without a world of futility parts wise, find one in as good of condition to begin with to start out. You can still easily find (just about, excluding the exotic models) any of the Pontiac, Olds, or Buick G bodies in near mint condition for $7k or less. Chances are if you buy one of these same cars in ugly condition for $1K, you'll end up putting much more than $7k in to it if you want new sheet metal and everything else cosmetic, if you can even find the stuff or more likely you end up with a body all full of Bondo which has never been something that set well with me on a car knowing it's there.
-UT-