After searching online for a replacement thermostat for my RVF I found no information other than using a genuine item.
As the genuine unit is comparably expensive and no aftermarket replacement listed I went about trying to find something suitable, at least in Australia.
As I'm always looking for an alternative what I have come up with is a Tridon brand, part number TT239-180 fits the bill perfectly and is readily available over the counter at my local auto parts store. A trap for young players is that Dayco list an equivalent to the Tridon as part number DT26A but this does not fit. It is not offset like the Tridon (and OEM) nor does it have the bleed hole. Just make sure you go the Tridon part and all should be sweet

Good find. Tridon appears to be an Australian brand; cannot see any for sale outside Oz, unfortunately. http://www.tridon.com.au/ However, it looks like they are made in three versions: 180, 185 and 192-deg C., so if a source can be found outside Oz, it would be a great find!

Ciao,

More searching suggests that the RVF part (19300-ML7-003, a very common Honda part, used on VFRs, Blades, etc.) is the same as the Kawasaki thermostat (4905 41059). Amusingly, CMS has both of these OEM parts, with the Kawasaki part being sold for much less...

Ciao,

Don't know if it helps the UK/USA guys but the Stant equivalent is listed as ST20-180
Don't have this brand here to try so dont know if it will work or not.