Aardvark International has lots of mirror parts but I don't think they have much for Lucas. Lots of Talbot stuff though if you're looking for outside mirrors. ( and let me tell you, if you hold an original Talbot in one hand and a repro in the other, no comparision!)
Tony Branda sells a mirror that I think looks pretty close for the interior. He says it's the correct mirror for the center (Lucas) but it's a repro. Short of finding an original on eBay, I think there isn't any made now. I think the front side should be black wrinkle finish but I know there's been some discussion about that in the past. Might do a search.
Anyway, here's Branda's site:
http://www.cobranda.com/corevimi.html
Cobra Restorers also sells a repro.
HTH,
Larry