There are only two gaskets on this carb, the bowl cover gasket, and the manifold gasket at the block that you mentioned. You can cut your own with material, a punch set, a pair of scissors, and an exacto knife.

New old stock gaskets are still around, you just have to find out who has them for sale. Here is one source to check http://www.ganotech.com/

This website has lots of very helpful information http://pochefamily.org/outboard/