If you have to you could just make the gasket yourself, Steve, like crazygn mentioned. I did it for the vaccum block gasket on top of the TB (you wont find that one anywhere!). Advanced Autoparts has roles of the stuff, not expensive either ($5 ?). They have it out in the isles.
Also, if you want, first try calling or going by the dealer on Monday. They probably have that gasket, (just not the vac block ones). Try Lou Fusz Buick/Pontiac/Olds at Page and Lindbergh, mention their car&driver add and you get wholesale prices (800-325-1492). You dont necessarily need the part#, they bring up pictures/diagrams on there computers from the old service manuals and pick the part (#) from there.
P.S. funny, I thought they had that gasket at AutoZone or Advanced. You say that they are the wrong size? I guess I wasnt paying too much attention, because I was primarily looking at the vac block gasket in the kit, which definately isnt the right one!