Pro 6 Power Supply or Upgrade Box

There is a seller on eBay that has them.  They used to be a lot more expensive than a more "do it yourself" approach, but no longer are.

The legacy 6-bay units all use an SFX format power supply with standard wiring except that the 24-pin cable is longer than typical and there are 3 4-pin MOLEX hard drive connectors (which used to be common, but no longer is).  While the original Seasonic is a 300W supply, it has more 12V (for the drives) than most 300W, so I recommend you go with at least a 350W, or even a 400W.  A 6" (15mm) 24-pin extension and either 4-pin Y cable or SATA to MOLEX adapter(s) will also be needed if you go with the  standard option.  Or, you can remove the 90° Molex connectors from the original and re-wire the new one (they are push-on IDP type).  I usually do that because it makes it easier to get it all in without worrying about the cables blocking the air flow or interfering with the fan blades.

If all you want to do is power it up long enough to recover the data, you can use a standard ATX12V supply externally.  But make sure you use masking tape or something to cover the opening the cable goes through and the original power supply fan hole so the main fan draws are properly through the unit.  If you have such a supply on hand (maybe from an old retired PC), you can try that first just to be sure the supply is the problem.