I'm in the midst of my first DiY light, a scaled down, primitive version of the Battlestar Ganjatica. Since it's my first attempt, I didn't stress over getting top bin COBs. I ordered most of the components online - COBs, drivers, CPU coolers, DC power supply and COB holders. The aluminium for frame, wire, screws, eye hooks for hanging, assorted connectors and all came from local hardware stores, thermal paste from a place selling PC parts. There are other online venues, if you know the specific part you're looking for, it's easy to find online.
Instead of a pre-made kit, I'd recommend starting with Gaius' Ganjatica plans. He lists everything you need (and where you can order it from, pretty much where I went), the only issue I've had so far was puzzling out how to wire all the DC power to all those tiny wires on the fans, but everything else has been pretty straightforward so far.
