I was putting my Columbian 603 back together and one of the pins was not going in so I was backing it out and it had broken! Is there a source for these somewhere? It measures about .2”
Perhaps you could go to your drill index and see if the shank of one of the drills matches the size of the hole. If it does, you could make a pin out of a drill bit, if the shank is long enough. If it is too short, at least you'll know what the pin's actual diameter is, as you continue the search.
Me personally, I would not put a hardened pin in there. The pin sees little to no force under use and the next guy may have to drill out the pin so be nice and use mild steel.