Hey. Sorry if I stated wrong size for the nut, maybe it is 14mm. Well, gee, sorry you're having this annoying prob. There IS another nut on top of the stalk you get to by popping off the little black plastic half circle cap at the angle in the stalk. I've looked at it but think it would be hard to tighten. You could try.
I think I've seen accesory mirrors at either the Kymco Global or Kymco USA site. They're chrome or stainless as I recall.
Some day if I ever get around to it, I'd like to do a mod which I saw on youtube. It would involve finding a pair of old style Xciting mirrors -- the contoured aerodymic ones that mounted on the fairing. I saw a vid in which a fellow made mounts that went up under the edge of the black plastic windshield edging. Turned out great and no drilling of the fairing needed.