I have also shifter kart and the pitch that they use is 428.
You will find easy in the web 2 piece 428 sprockets for the thickness of your rear axle. http://sharkshifter.com/zc/index.php?main_page=index&cPath=96
The front sprocket with 428 pitch for the NSR engine is an other story. J T sprockets site has drawings with dimensions,check out if any others bike sprocket is compatible. If not,there is a way to make the sprocket that you want but this must be the last choice.
For the chain,the shifter karts use non o-ring and the best chain which can handle their power is DID-428NZ.
Check here the chains specs http://www.didchain.com/chainSpecs.html
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Owner of : Honda NSR250 MC28 95sp colours / Honda NSR250 MC18 R6K SP / Honda RS250 NF5 89 in boxes
/ Honda C50 12V cub / Honda C50 12V super cub Japanese version /Yamaha XT600 89 benetton