You can buy a tin of both caps (#10, #11), one will fit perfect and the other will most likely need a little pinch to oval them up a bit. Trial and error. You should be able to find .451, .454, and .457 round ball if you look hard enough, although I would guess .457 is not what you're looking for. If you can get a handful of .451 and .454, see if the .451 shaves off a little ring of lead when you seat it in the cylinder....if not .454 is probably your best bet.
As for powder, anywhere in the 18-25 grain range of BP or Pyrodex P topped off with cornmeal to about 1/4" of the cylinder top should fit the bill for nice shooting loads recoil wise.