Aimee,
Yes my vet stocks it on the shelf. and I buy it from her. I don't know if you can buy it elsewhere, like at a pet shop or what. but the main reason I buy it from the vet is I know that she has a pretty quick turnover in stock so I know the shelf life on it is going to be less than say a big chain that keeps it wharehoused somewhere waiting for orders from the store.
Now I guess it's true that it could be wharehoused where my vet gets it from too, but it works wonders for me. I have 2 fosters, 1 adopted Yorkies, and 1 mutt that is my daughters, and 1 pittbull pup that is my sons and they all potty outside, play outside, stay outside for good lengths of time on sunny days and we have absolutely no flea problem. Also all the dogs sleep with their respective owners. In my case my baby Pita and my 2 fosters sleep up on the bed with me.... No Dear Hubby here dang it!!! But they more than make up for his whining butt anyway! Plus they give me sweeter and more sincere kisses

I don't treat my yard at all, and it hasn't been any kind of a problem. I think the darn fleas have to get a foothold or something before they really become a menace and if you keep the dogs sprayed and bathed the fleas arent' going to stay somewhere they can't get anything to eat!