Ballast help for Mini Fridge

Hello, first post here. I just bought a Mini Red Bull Fridge on craigslist and the fluorescent lights are out. I narrowed the problem down to the electronic ballast. I cant seem to find what type of ballast i need nor where to even get one. Here are the specs on the fridge
It Has three lamps, two are f8t5cw, and one f15t8cw. runs off of a standard 120 volt plug. My problem is i cant find a ballast that has the ability to run off of different light bulbs. My original plan was to find a 4 bulb 15 watt t8 ballast and cap off one of the leads. But i dont think you can put a 15 watt ballast and run 8 watt bulbs. Any ideas guys? I need to fix this thing before i head off to college.