Searching for 42cm 1:35 ammunition

It would appear that the RPM kit is the only game in town. What's worse, is you only get one round. You would quickly drop a big chunk of change trying to supply your piece with a suitable number of rounds. While I have little affection for RPM kits, I don't see much alternative. I'd also invest in a silicone rubber casting kit, if you don't already own one, and cast your own duplicates.