take a look through your local phone book and see if you can find a builders discount house in your area, or even a builders salvage yard is good but you need some DIY skills because the stuff you get at the salvage yard might not work out of the box, as it were.
if you can't find one then you'll need to go to Lowes or Home Depot and pay full retail.
anyway, i'm assuming you're on a real tight budget so i'd suggest you look for one of these multiple bulb bathroom vanity fixtures that you can add splitters to to double the number of bulbs you can use.
here's a couple of pics of one of my old light bars from back when i was still growing with CFLs (i grew with nothing but CFLs for almost 2 years) and if you look close you'll see i paid $4.88 for these fixtures from the discount house.
bozo