PCB for high power LEDs

I’m looking to build a printed circuit board for high power LEDs, like the CREE XP-E. I need to make several sizes, the max being 6x8 inches. The boards will contain 36 (or maybe more) LEDs, which at full brightness will draw over 100watts (though they won’t all be at full brightness). Efficient heat removal will be very important. Since the heat sink will need to be on the back the board must conduct heat through it efficiently. I’m assuming a metal core board with a heat sink on the back side. I’d like to avoid using LEDs pre mounted on stars because of the spacing (and cost issues). I am thinking it would be best to reflow the LEDs directly to the board.

Is there a way to make metal core boards at home? Any economical services for limited production runs?