Bill --

There's a very active group of British sports car enthusiasts, and many excellent parts sources for MGs, Triumphs, Austin-Healeys, Jags, etc. Many, many different flavors, sizes, shapes, and models of SU carbs were used on the British cars. If you can't find SU parts from the normal Volvo sources, consider trying the British cousins.

Here are a few links:

British Car Parts

British Spares West

British Masters

British Sportscars

Moss Motors <== Very good parts source.

Fixing a Triumph <== Interesting and organized links, including SU's

List of MG specialists in US

A "Book" on Jags, it might include information on SU carburetors.

Links to British car parts

Of course, you can always make a new gasket from gasket paper..... I once made new gaskets for the SUs on my '50 MG from the cover paper stock of a magazine -- National Geographic, I think (they're the best!).