Smoke shops have exploded but it isn't clear to me that there is higher availability - every convenience store in the US sold cigarettes and most still do. Even pharmacies like CVS/Walgreens used to sell them. I think just now you have dedicated storefronts for certain types of smoking products.
I think the difference is that cigarettes and packaging were almost completely uniform - the same size and footprint regardless of brand. As such they were relatively easy for stores to maintain. I think the sheer variety and variability of vaping hardware and packaging almost requires a dedicated smoke shop to be able to service customers.
interestingly you had head shops(paraphernalia) before legalization. everyone knew what they where for but nothing illegal until it was used for that specifically. you can even buy crack pipes in some of the seedier neighborhood stores.
