Haven't seen anything with that much power yet, but it could be coming down the road. Current models offer 75 watts from the PCIe connector. Some newer models may come with 150 watts. Still stand by the fact that it's too expensive to be worth it though.
Your idea of a gaming PC and 13" macbook is probably a better idea than an external GPU.
I found this one:
http://www.magma.com/thunderbolt.asp
But that doesn't seem to yet be available. But also that's not what I was thinking about, which was probably the upcoming ViDock, which will likely come in variants up to 225W as well. But considering the prices are likely to be close to a grand BEFORE you start thinking about the graphics cards, a dedicated gaming PC is still obviously the best solution.