Since these are just basic pins, (with round ends that stick slightly above the frame surface), I would make replacements from finishing nails if I were you. You can easily turn them down to the proper diameter and round off the ends with sandpaper and a hand drill if you don't have more sofisticated tools.
If you simply must
have original (or exact reproduction) pins, then check with David Chicoine Old West Gunsmith (and author)
. If he doesn't have any, then they probably can't be found. I have a few, but they are happily residing in the frames of the guns they came in!