You can get 48" T8s in 40W variety: Power Glo Fluorescent Lamp > 48" (40 W)
That's just an example. I'd buy them at the hardware store. I use daylight spectrum 40W T8s from Menards in the shop lights in my garage.
With good reflectors, I think you'll get better lighting with the T8s. They're smaller so there's less light lost to restrike and it's easier to get better reflectors into the fixture.