Did you post a pic on the FB group recently? (I can't find it now)
All pistons would need to be closely inspected!
It's possible just one cylinder went lean for some reason and got damaged. (vacuum leak, ran too hot, etc)
Ring lands can break off if the ring end gap is too small.... the rings get hot and expand, the ends butt together and the ring binds in the cylinder. When that happens, the topmost ring land becomes the weak link and can break off. Rings will have shiny spots on the ends and cylinder walls will likely be scuffed.
Or detonation/preignition can can damage the top of the piston. I've seen broken piston domes from detonation too.
You could try eBay, T/A Performance or the Martins at Centerville auto for pistons.
I do have a set of Badger 425 +0.030 pistons I don't plan to use. They were pressed on/off of rods and have a little scoring on the pins and pin bores, but never ran.