Look on eBay. they show up from time to time. You want the one with a rubber grommet in the back of it with the wire running through it. NOT the one with a connector on the back.
Top tip: when hunting there select "closest first" then you dont have to weed through the huge numbers of auctions for absolute junk made in India.
Don't forget there is a 1/8 foam/rubber gasket that goes under the light on the fender. Easy to make, I have a photo somewhere of a NOS one I bought years ago.