Good source for 10" Drums?

Nope, you can't change the brakes to larger. The centering register for the drums is smaller on the small bolt stuff, plus the flange is closer to the axle housing flange. I have heard that b-body 10x2 brakes might fit, but you've still got the centering register to deal with. In my opinion, that's why it's better to do it right in the first place with all big bolt stuff not redrilled a-body axles.