I'll be frank, I never, ever would have thought it could be illegal to make BP. Just a chemistry project and experiment. It is far, far easier, and far less dangerous than people here are suggesting it to be. The big difference between "green" powder, a nearly useless mix of the dry, powdered ingredients in proper proportions (likely what mythbusters made, didn't see the episode) and real black powder is the milling and corning. You press it from a wet mixture in a fixture on a jack in a press into a puck using pipe and a roundstock piston. I don't see why it would be illegal here in small quantity as an experiment, but I'm no lawyer and if it is, my god are were a babysat society. I suppose those living in Toronto shouldn't consider it but a lot of Canada still lives in the country/north. Making it is too labour and equipment intensive to make sense for anything more than a science project though, you'll pay 10x per pound more making you own.
Corning to be clear is the pressing of wet powder mixture into pucks or pellets which are essentially wrung dry under pressure, then allowed to fully dry. This process, and proper milling before this of the mix (for the home brew types, typically done in a rock polisher [mini-ball mill]) one ingredient at a time, then mixed green in the mill with no balls for a short time, then wetted and corned. The ball mill for safety can be turned on remotely by extension cord and sat in a depression. You'd want to be careful of static when opening green mix. Hope that's interesting, if you try it and get in trouble, I'm only chatting not giving advise. If anyone wants saltpeter I have a source for plenty of pure KNO3 I can point you too, nothing special or illegal about it.