I know that this is a bit of a necropost, but I ran into this same problem a while back (holster was borrowed by a parent and left at their house; mom is a chain smoker). Long story short, I had a pair of Galco holsters and a Desantis holster that smelled to high holy heck.
Cleaned them off as best able, which took care of some of the smell. Used Febreeze (be careful with this stuff since it has the potential to color/damage the leather), and then I put the things in a medium sized tote with a generous helping of baking soda (I did not have the baking soda touch the holsters; holsters were on a separate pad). I checked them at the end of the week and a good portion of the smell was gone; gave it another two weeks and afterwards I just let them sit outside for a bit. No issues any more.
Yeah it's a bit complicated and time consuming, but tobacco smoke is a devil to get rid of.