I bet Global does carry the touch up paint as BSM is a very popular color.
But really the tiny spot that is chipped won't be large enough display the color flecks embedded in BSM.
Most any black auto paint will do as all you are doing is hiding the white undercoat layer that is showing through.
Your car is not going to rust ...... this is just a little cosmetic touch up!
"sometimes you're the windshield .... sometimes you're the bug"
2014 328i Mojave Metallic
2009 328i Black Sapphire Metallic
2007 328i Black Sapphire Metallic
2007 Honda S2000 Berlina Black
(Hey Jim... am I diversified?)