The flavor extracts found at grocery stores is probably too weak and too many additives to be good for vape. If you are talking about the super condensed type flavors found in the cndy-making, cake-making aisles, it is probably ok. These are usually sold in tiny bottles, since the cooks only use about a drop of it in recipes. The easiest way to get flavors, IMHO, would be the internet. Plenty of good vendors with good prices. Shipping price isn't bad, and it takes only about 4 days.
PG, I've heard, can be bought at tractor or farm supply stores - it is used for medicating cattle. You can also pick up some syringes at the same place. I find it easier, but more expensive to get it off the net.