It,s been awhile ago someone listed an automotive diaphragm as a direct replacement but don,t know if it was for a 40 or not so maybe they,ll come back to you on them.
Check Willies site http://www.westernfarmcollectables.com/
He has diaphragms for sale but I can't tell you if it's for the forty.
I got mine from John Matta the one Willie has is for the potmetal fuel pump for a 22. Item 5![]()