When I added a pump to my B, I reused the old gasket with some RTV silicone. If I recall correctly, there aren't any tapered bearings on the assembly so if you don't have the gasket you should be able to get away with just using the silicone.
There is a guy in Romulus, NY that has a Allis grave yard and also deals in aftermarket parts. His name is Sheldon Sharpe and he will probably be at the Pageant of Steam next week. If you talk to the guys under the Allis tent they can help you track him down.