You listed everything and more. I instantly thought of Kanter. Well never mind there... So I had a set of pistons made for an older 4 cyl mercruiser boat motor. The engine builder said they were not much more than over the counter pistons. He had trouble finding only 4 pistons and no parts places would break up a set of 8. So he had them made out of California.
M and S engine in Ponderay ID. Greg is his name. He has built a couple engines for me and some other machine work. He is slow but meticulous. The engines he did for me all run like a sewing machine.

You are left with sleeving and STD bore pistons, waiting for ebay to have oversize pistons pop up, or like some would suggest, repower....
I would keep looking and try to be patient. You never know.