I finally got .410 shells…available at Buds. Winchester AA for $0.70 per. More expensive than I am used to, but at least finally have some…
https://www.budsgunshop.com/search.php/type/ammunition/caliber/10000867-410+gauge
https://www.budsgunshop.com/search.php/type/ammunition/caliber/10000867-410+gauge