The chances of finding an actual Izawa bolt and matching it to your rifle is about zilch. My Izawa 4th series has a small 2mm dot along with regular Nagoya proofs. I've had 3 Izawa 4th series rifles and everyone had the extra dot proof mark that the regular Nagoya rifles did not. This info the average Joe wouldn't know.
Thanks for the info Big Ed! ("This info the average Joe wouldn't know". Count me as part of that group) There's a couple of bolts on ebay I've been watching. I thought I'd give this forum first refusal.