Req: Help/Advice on Cromemco System

I have most of the stuff to put together a System 3. I have the card cage with the 21-slot motherboard and a bunch of cards. The manuals I got with the system include the Cromix manual, I have more than 1 64-K RAM card and at least one TPU, so I believe that mine was a multi-user system. I would like to put this back to near-original, but need a case and power supply. Since I have been unable to find any power supplies which provide the +/- 8 and +/- 16 volts, I just thought of an idea the other day of using a PC power supply and shorting out the on-board voltage regulators to allow them to work at the +5V and +12V of the power supply. In order to do that though, I would need a small (3-5 slot) motherboard to test a couple of cards together. If anyone has any of these available, I would be interested in obtaining them. I do not have much money, but do have some other old computer stuff that I can trade: a VAX Station 2000, an old Sun workstation, many, many old PC parts and systems, lots of electronic parts, lots of microcontroller stuff including several Dev Kits.