Well, it seems options abound.
Good to get some clarifications on size and application.
While working with molten metal and sand casting certainly has its' attractions, (at least to me), it seems that from an efficiency point of view machining from a solid block of bronze might win out in the end.
For instance, a piece of C95400 aluminum
bronze, 2 1/2" x 2" x 12" (enough for 2 gudgeons), is 112.64, plus shipping
, from Bravo Bronze,
C95400 Flat Bar 2-1/2" Thick x 12" Wide - C95400 Aluminum Bronze - Shop By Alloy - Shop Alloys
I'm not sure this is the best alloy for the application, but I'm sure a call to them would steer you in the right direction.
Regarding machinability, in my limited experience with bronze, it seems that bronze was a little easier to work with than stainless, though that is probably a function of the alloy one's working with.