have you tried to come up with the Briggs part number for the carb. kit on Sears Parts website? They have some of the really old stuff on there.
If you can come up with the Briggs part number about any Briggs dealer can tell you if it is still available.
I would check Ebay for the air filter. If yours is the one with the funny offset intake, You may have to search for it as a David Bradley part.