If I have time I'll take a photo or two of the ones that I do have in the other B-15C Mod I own. Modern Alpha MA-1's (at least the U.S. made ones) have a plastic version in their pencil slots. These look pretty much like a Bic pen top without the 'prong' to hook it to something.
I tried Charles at HPA and he was super helpful as always but said that without an original purchase receipt Buzz Rickson makes it very difficult to get spare parts. It has to be treated like a warranty claim.