Seems these have been hard to find, at least in the U.S., up until now:

K100RS Right Turn Signal Lens

I ordered one and it's really solid, fits perfectly and looks great! 

They have left ones too, by the way.

So you pay $29 for it from EME on EBay but if you go directly to their website it’s only $25!

I put these clear ones on my RS. Look much smarter IMO.

https://www.ebay.co.uk/itm/323897269789

(Worked out slightly cheaper than amber lenses from Motorworks when I bought them. Price seems to have gone up a bit )