Try Underwater Kinetics, or the Storm Cases at Galls. I don't know if they have the sheer, raw strength and the boyancy of the Pelicans and Otters, and I know they don't have the Peli's bells and whistles, but still water tight.

Might be worth a shot.

If all you want is water tightness and don't mind the weight, scrounge the surplus sites for 50cal ammo cans.