Western Gun Parts - but they always courier, and that gets expensive. If you have a friend in Edmonton who could mail one to you it would drop the price to postage and a beer next time you saw your friend.
Measure the diameter (use a caliper or borrow someone's caliper, get it to within .001) - get a piece of rod the same diameter - cut it to length, polish the ends, dip it in "cold blue" solution. It doesn't need to be hardened material, but you may be able to find a drill with a shank of the right diameter - cut it off (with a dremel or grinding wheel - but you'll need to go slowly to avoid heat) and polish the end...
You could also get a nylon or other type of plastic buffer - to silence the rattling of the bolt hitting the buffer on recoil.
Just measured a factory bolt stop pin. Diameter 0.248, length 1.252. All in inches.