I can purchase .457 lead balls from two sources these are Henry Krank who stocks Pedersoli Italian manufactured balls at £24 per 100 or for cast balls for £13.50 per 100 both of these prices include postage costs, which you have to include if you are going to get the true cost.
To be honest I can't be bothered to cast my own,
I am more interested in the chamber size problem, if a .451 ball falls under its own weight to the bottom of the chamber, is an additional .003" enough to ensure that the chamber is sealed well enough to prevent a chain fire?
I use Wonder Wads and I don't have a problem with them, but with any muzzle loading revolver the first line of defence against a chain fire is all said and done the ball and it's capability to seal off the chamber.
If necessary I will ream the other chambers out to match the size of the largest one, what surprised me was the different manufacturing tolerances they allowed that passed their inspection process if indeed they had one!