Best bet is eBay. Be sure to check that you are buying an ECU specifically for the year and model of ZX-6R that your own. It's easy to buy the wrong one, and that won't work at all, and is generally unreturnable being an electronic item. Note that different countries get different ECU versions.
Be sure to buy froma reputabel source with a great eBay customer satisfaction record, as some ECUs turn out to be "bricked" - being sold by an individual or vendor that either did not check it or know it is bad and just want to unload it.
Nice bike by the way. Paint looks fabulous in its quality, and the seat upholstery is impressive.
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