Why would it have been difficult? Barbers could get natural stones from Japan, quite good ones back then.

Presumably australians tanned kangaroos for the last several hundred years.

It's possible that it may have been difficult at the retail level, but the trades have always had access to nearly anything accessible from around the world. I can't find anything about it, though, only barber guides that suggest shell cordovan is the best leather for a strop.