I emailed the Spectra company, who makes a ton of repro gas tanks, about our non-existant options.
He said they don't have any plans to make one at this time, due to low demand (bah!). I did give him the approximate dimensions of mine, and he found me one with pretty close specs:

Tank from my 1969: 36 x 28 x 9
Tank from 76-77 Grand Prix: 39.75 x 26.5 x 10

The only thing I'm kind of concerned about is the raised area where the fuel pump goes in. The filler neck can be cut/welded back to the original shape, or I can re-use my old one in there.

Whatcha think?

 

That tank is four inches wider than the original and almost guaranteed to interfere with tailpipes, esp if you have the resonators.

Also, that vapor dome is going to require trunk floor surgery or spacers to ensure enough clearance, which is going to drop the tank bottom even closer to the ground. It will already be an inch lower. 73-77 GM cars have a clearance dome stamped into the trunk floor.

You cannot convince me that a 76-77 GP is a more popular car than 66-70 Toronado. It has to fit something else for them to tool up and make it. Probably fits all the A and A-specials.

 

I ordered a new replacement tank from Original Parts Group for my 67 Cutlass. It fit perfectly and had all the correct vent ports too. If I remember correctly the tank was made in Canada.

This was one of the few aftermarket items that actually fit without some tweaking.

 

No doubt that was a Spectra tank. Most of the resto specialty places sell them. A-body tanks are readily available, but we big-car guys have no good options.