I used to buy his nickel round wounds when Jimmy was still in NYC. I believe he said at the time that they were made for him by D'Addario, and that the idea was to make a string that was a combination of his two favorite nickel strings: D'Addario XLs and Zon Ultrasonics. Don't know if the current formulation made for him by Labella is the same, or based on the same idea.
A while back, I did buy them once from his website after he had moved to the west coast, but with a price tag for a 4-string set of just under $30 PLUS something like a $12 shipping cost (!) . . . you get the idea. But I did like them more than any other nickel round wound I've ever used. Also, I am familiar with both the XLs and the Ultrasonics, and I can say that they really did sound like a combination of the two.
If Bass Strings Online is offering them for a more reasonable price shipped, then I will buy them!