I was at Fry's Electronics yesterday, and I happened to notice they had 18650's and CR123's, along with a lot of other stuff I didn't pay attention to.
I prefer to buy my
batteries online from vape-stores, usually from the same place I got the mod. But in an emergency, it's nice to know where you could pick something up right away.
For the 123's, I'm told that those are commonly used in cameras, so camera stores probably carry them.