Are your cartridges intended for a '51/'61 Navy percussion revolver fitted with a Kirst conversion cylinder? In which case, casting your own heeled bullets may be one(if not the only) option. If you don't already have this info, the following may be useful: Old West Bullet Moulds. Eras Gone Bullet Moulds. Accurate Molds. Old West Bullet Moulds and Accurate Molds do ship to Canada. Though this Covid thing may cause some delays. I have not ordered from Eras Gone, so can't say for certain.
Another option, is to load .38 Short Colt with .358" hollow-based wadcutter style bullets. I believe Hornady lists these. Not the best solution, but workable. If you prefer to purchase your bullets rather than cast them, this may be the way to go.
By the way, reloading dies for .38 Short Colt(heeled bullet), are available through Old West Bullet Moulds. For other(inside lubed) bullets, Lee Precision lists .38 Long/ Short Colt dies.
p.s.: In the October issue of SASS "Cowboy Chronicle", Part 1 of a 2-part series on cartridge-firing converted C & B revolvers(Including .38 Short/Long Colt) is featured. This may be of interest.