I've got a couple of grey market 250's that I've had to source parts for...a NSR and a TZR, and I would think that parts for the KR would be obtained in similar fashion. What's no longer available from mother Kaw, could be obtained via YahooJapan or eBay UK, NZ and thru the various forums where owners of these bikes linger. There are many parts for the TZR that cross reference to other Yamaha models, FZR, TDR, etc. It may the same for the KR's.
Companies like Tyga Performance are big on aftermarket and OEM parts for the NSR's. RSCycles also sells lots of parts for the TZR's, as they still race TZ's and order parts from Japan often. You may want to email Steve @ RSCycles (
rscycles@gmail.com ) and ask him about availability of parts for the KR's. I'm not really sure how popular they were.