The schematics for the Raspberry Pi are availableschematics for the Raspberry Pi are available at raspberrypi.org. The challenge is to find a source for the parts.
For incorporating a computer such as this into a product, I have heard that it is easier to use a Beagleboard design such as the schematic for Beaglebone BlackBeaglebone Black. The information needed to build a Beaglebone Black is freely available, and you might be able to find sources for the parts.