One Ebay seller has had new ones (Apple Service Parts) for sale for $75 + shipping for a couple of years. But it doesn't include a heat sink, which could be an issue if you're going from single CPU to dual CPU.
I have the dual 1.25 MDD, the HS Appears to be extruded.
Right now I can still boot Mac OS 9.22
If I found 1.42 cpu's for this thing, wonder if Mac OS 9.22 would have any issues?
all i saw on ebay was this one running @ 1.40
http://www.ebay.com/itm/PowerMac-Mac-MDD-G4-DP-Dual-1-40GHz-CPU-Processor-820-1470-A-/400328914870?pt=CPUs&hash=item5d357677b6
Ah, thank you. Good to know. I had heard it both ways, so was not certain.The aluminum heat sinks on the single and dual are identical.