Blackhorn 209 powder is a synthetic black powder that is made for use in a modern in-line rifle. The 209 refers to the type of primer that is needed to get reliable ignition.
Basically, that makes it unsuitable for the traditional side lock type of guns which use a small percussion cap for ignition.
There are several other synthetic powders on the market that will work rather well in the traditional style guns. The oldest is Pyrodex and another one is called Triple Se7en .
While these powders do work, nothing beats real black powder for speed of ignition and reliability in muzzleloaders.
While most gun stores don't carry real black powder, some of them do but you will need to ask the store owner or manager if they have it.
That's because, by Federal law, they must keep it locked up in a powder vault. Because it is locked up, often the guy at the counter won't even know they have real black powder. That's why I suggested talking to the manager or owner.
Real black powder can be bought on line and shipped to your door from several different places.