Lots of the common 12ga trap and skeet powders make great pistol powders for our gamer loads.
American Select is a favorite for every thing from 38 short colt/9x19 to 45acp. Others are red dot, promo, 700x, e3, clay dot, nobels GM3…you get the idea.
For a Plan B powder check out what your powder source has in stock. Shotgun powder usually has good published load data for pistol loads, too.