Looking at newegg, here is what I have found:
I noticed none of the intel or amd desktop sections list any motherboards that explicitly support registered ram.
However, if you go to the motherboard-->server motherboards--> filter by registered RAM support, you will get a list of boards. Many boards state xeon support, but also mention support for other desktop processors. You can go through those and see if any of them support what you need.
But, their is one problem I see. Just because the motherboard may support registered RAM and multiple processors might not mean all processor/motherboard/RAM combos may work together. Because of the integrated memory controllers with today's processors, you may have to get xeon or opteron workstation class processor to get registered RAM support as that is normally a workstation class feature. I am not sure which ones do and don't. Be sure to do your research on the board you choose and the processor you choose will work together with registered RAM.
Hope you find something that works for you. Let us know what you find and works for you.