try looking thru the HAMB, the P-15/D24 site and the Chrysler club sites.
I do know that the big 6 is a lot harder to find speed parts for, but they are out there.

http://www.jalopyjournal.com/forum/showthread.php?t=259263&highlight=chrysler+flathead

http://www.edgyspeedshop.com/products.html