I have been tracking this one down for a long time now. I got very close when I found out the UK Roland users group had stock - but they have gone bust!
Someone has got stock of these but I don't know who. I spoke to a service engineer in NY, he said he thought the kit was made in LA somewhere.
It's basically a speed increase on the processor clock (like you can on PC's) but its not just a replacement clock, there is a board too. It tightens the MIDI timing up (why I want it) and speeds processing time. No new features though.
If anyone knows anything about these kits (even a list of parts) please let me know.