Depends on the amount you want to invest in.

To buy by the gallon then online is probably the best, but if your only looking for like 16 oz's
or so then you can get your VG in most any store such as wal-mart, Kmart, Longs, Rite-Aide
rex-all etc, usually in the pharmacy dept.  You can also get some Loranns flavorings in the craft section of wal-mart,  just make sure the ones you choose are water based, I think the citrus flavors are oil based. 

For PG you can find it in your local farm supply/feed store.  But I would suggest you read the post under General Topics in this forum titled "Propylene Glyco really explained"
Personally I use PG for my mixing and after reading this I definatly will continue to use it.

VG is a carcenogin, according to some studies. I don't care how much smoke you get from it......

I'd be intersted in a link to such studies?

It was on the big forum over a year ago. I think it was done by the University of Vienna. It was a post by "Ludo" the owner of Janty.That was the "big study". I have also seen other posts, but not that I could refer you to.

Thanks - I'll try and track it down - I'm not that bothered personally as I prefer PG, but most studies I've seen rate VG as a "safe" substance.