JDW, do you know the amperage requirement for the -12V rail (stock)?

These models would also fit if a quad PSU is not necessary:

120W CUI - 5 VDC @ 15A / 12 VDC @ 6A / -12 VDC @ 800mA

http://www.digikey.com/product-detail/en/VSBU-120-T512A/102-1272-ND/650836

125W Power-One - 5 VDC @ 16.5A / 12 VDC @ 5A / -12 VDC @ 500mA

http://www.digikey.com/product-detail/en/MPB125-3000G/179-2277-ND/1021432