Hate to say it, but GM did not sell that part separately according to the parts manual.
It was included in a kit that also includes the fittings, injector filters, etc. Likely too costly for what you need, if they even sell something like that today.
Look for a TBI gasket kit, or a TBI injector gasket/filter kit, something along those lines. Also, check ebay for vendors selling TBI gaskets and/or rebuild kits, and ask them. The gaskets themselves are obviously available, it's just a matter of finding them without having to buy a complete kit.
They appear to be teflon to me, but they are pretty darn thin. They'd be hard to make without a proper punch set. IIRC they are pretty darn small diameter flat white seals. Someone can confirm...may help you identify them looking at kit or gasket pictures. AFAIK they weren't used on any other GM product (that wasn't TBI).
Unsolicited advice, but I'd not be too set on running a fuel pressure gauge unless you absolutely need to monitor it all the time...if that worried, carry it as a trail tool. They are easier to run off the fuel line at the fuel filter for diagnosis or pressure setting of an adjustable regulator. But that's me...I know plenty like their fuel pressure gauge.
As another unsolicited factoid, the horrible electronic mystery known as the throttle body has about 1/3 the parts of a quadrajet. The things you notice in the parts manuals...
