Measure the stroke required by measuring the distance from mount point to right hand fork tube on full left lock and on full right lock. The difference will give you the minimum stroke required. Then google steering damper and you'll find lots. I have an Ohlins on mine, but mainly due to having it left over from a Ducati. There are always plenty pedalled on Ebay, but make sure it's straight and a rebuildable type so you can have it rebuilt if it's shagged.