Looking for the same thing i scanned eBay and seen some. Just looking for reviews on which ones are good.
Vista Cruise Universal Cruise Control - Metric Cruisers with 1 inch Bars
Why fleabay? These are for the wrong bar but 30 seconds of Internet trawling should get you what you're after.
I've never used one of these but I know several that are happy with this one too: Throttlemeister - Home
motorcycle cruise control throttle lock | eBay
This is a metal version of the plastic one. I think it will be much more durable, it wont slip because of the rubber band. i cant wait to give this a try