Colt experimented with a Single Action Army chambered in .41 Magnum, but chose not to market it. I think the decision was mostly based on the cartridge's relative lack of popularity combined with it's association with a well-known rival down in Springfield, MA. In a single action the cylinder walls would be fairly thick, and moon-clips wouldn't be necessary so the full case head would be supported. Most of the demand for 10mm revolvers comes from the "combat game crowd," and there's nothing wrong with that, but a demand for the 10mm in cowboy revolvers would be, I think, pretty limited. Same with the .38-40 round.