Updating this thread, since I read it whilst looking for info...
The (supposedly) correct cable for my bike, (2008 XB12XT) is Buell/HD #38726-06C, as noted above. I found it is not readily available anywhere online. St.PHD and Twinmotorcycles list the part, but I didn't check to see if they actually had it.
However, my local HD Dealership parts guy said they were in his system. Current cost is $134. I have one on order - I'll check to verify correct fitment when it arrives.
Reason for ordering new - my cable is probably the original one. I had been having clutch issues, and noticed the release lever was reluctant to return to 'fully disengaged' position. Which may have had some effect on the release bearing (different thread).
Yesterday I took the cable off the bike, and found that is was not moving freely. Probably due to over-exuberant application of lube - which the teflon-lined cable doesn't need. Or appreciate, apparently. Otherwise, it looked great. I guess I'll have a spare on the shelf!
So, using plenty of brake parts cleaner (and splitting the cable carcass at the adjuster) I got the cable moving nicely, with almost no drag.
Re-assembled, I made sure the lever was fully 'relaxed' (all the way to toward the rear of the bike), and adjusted the release bolt, then the cable length.
Taking the bike around the block, the clutch feels better than it has in a long while!