I'm in the same boat. My bike came to me with a 23/11 ratio drive (a genuine Veglia unit), but I'd like to replace it with a correct 20/10. I've not had any luck finding one anywhere, NOS or used. The only option seems to be the reproduction ones, and comments on them range from "feels cheap and broke almost immediately" to "feels cheap, but works fine". Since none of the repros have any identifying marks on the housing, it's impossible to tell if they are all the same, or if any of them are actually better than others...