Mike,
Possible that there are 10bore round balls available, but they would likely be pure lead and sized to function as patched balls in a muzzle loader.

You will really need to know the bore/groove diameter of your barrels as there is historic variation that depended upon whether or not the rifle was intended brass case or paper case ammunition.
Your easiest path is use that Tanner ball mould (may be that you don’t cast your own but can find someone that could do some for you?) and use those round balls to see how things go. I personally cast of 1-20 tin/lead for my 12/10/8bore rifles.

- Mike