The [schematics for the Raspberry Pi are available][1] 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][2] design such as the schematic for [Beaglebone Black][3]. The information needed to build a Beaglebone Black is freely available, and you might be able to find sources for the parts.

  [1]: https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/Raspberry-Pi-Rev-2.1-Model-AB-Schematics.pdf
  [2]: https://beagleboard.org/
  [3]: https://github.com/CircuitCo/BeagleBone-Black/blob/master/BBB_SCH.pdf?raw=true