Yes - the ultralite part number that fits the KX500 (252U-520-14GP or -15GP) also fits certain year models KX250, KDX200/220, KDX250, KLX250, KLX300, YZ250, YZ400/465/490, WR250, WR500, RD350, Banshee/Warrior 350.
Needless to say, a search on part number "252U-520-15GP" doesn't turn up anything... Talking with Renthal, turns up that it is no longer in production, though they do show it on their website as "out of stock" (for the last 3+ years!).
Probably somewhere, there might be one sitting on some dealer's parts shelf, but cannot be found through a Google search - Really a great quality sprocket, a real shame it is apparently no longer available.
Thanks again for the contributions, present and future.