Petco and Petsmart have D. melanogaster and D. hydei respectively. While IMHO the frogs going without food for a day or two isn't harmful (there's always plenty left in the viv in my case) I'd advise you to go out and visit. You may check specialist reptile shops in the area as well, but those are the two that I know carry fruit flies.
Oh, one more thing: always, always, always have a backup food source. Springtails, mini-mealworms (T. obscurus, not T. molitor), and confused flour beetle larva are all extremely easy to raise and can carry you through a week or two getting your fly cultures back up to speed.
If you're thinking that mini-mealworms wouldn't intrest frogs, think of a normal mealworm. Think of a normal mealworm with dark coloring. Now think of that mealworm dwarf sized. Now think of that dark dwarf mealworm on speed, and you'd have T. obscurus. These guys are fast and active, they'll run right off your hand if you let them. I got mine here: http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... tegory=301