For forum sponsors try Rustywood they do stock muzzleloader supplies. I've bought stuff from them, really quick shipping decent prices.
Otherwise, look up Hillfolk Musket Supply there in Saskatchewan - I haven't tried them myself but lot of good references.
All that said, honestly making the range rod, short starter and measuring containers is quite straightforward. I'd recommend that if you are really keen, I've never found commercial equipment to quite fit the bill - but to each their own!