Track of the Wolf in the U.S. lists a Lyman .715" round ball mold for $75.00 U.S.
You could melt down roof jack lead or whatever you could scrounge.
They also sell pre-cast .715" round balls (25 for $12.70 U.S.) but I don't know if the balls could be imported, being bullets by definition. The mold is no problem though.
Couldn't find a source for pre-cast .715" round balls in Canada, but the size is used in repro Brown Bess muskets, so they must be available from somebody.
Rusty Wood Trading Co. in B.C. has plenty of cannon fuse.