DO NOT SHOOT A STANDARD FLINTY LEFTY.
Getting the bits of frizzen out of your cheek is pretty straightforward- they are magnetic- but the bits of flint are much harder, and you may be mistaken for a Maori tribesman with the powder tattoos on that side of your face from the priming pan.
For the sake of historical accuracy, you might consider doing what His Majesty's Army did- find a large, beefy, ruddy complexion man with a voice akin to a foghorn, who will berate you to put the bloody firelock on the other bloody shoulder, you sorry bleeding handless clot! (or words to that effect)
Have seen a few left handed rifles, cannot recall seing a lefty musket. Of course, given enough time, money, and a fully equipped tool & die maker's shop, anything is possible.