If no one else answers with a better source, Ive gotten odd sized or NLA rings from a place called Otto Gas engine works. Or Otto something.
there is a website, but he’ll want you to call as I remember.
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I have a pair of pistons from KD twin that may/may not meet your need, Rings are solidly stuck in grooves and no piston pins. Otherwise they look ok. If you have pin that will fit into piston snugly that would be good to go, You are welcome to both for postage, An option in case nothing else comes up.