you could also try AV Camera in Bangkok, next to the Robinson's at the Sala Daeng stop on the Silom line. Just a hunch that someone there will know, because they have on display an incredible personal collection of rangefinders, from Canon, Leica, Nikon and Contax.
Alternatively (and not to steal thunder on providing another new forum) there are four rangefinder users from Thailand on the Rangefinder Forum,
www.rangefinderforum.com, two in BKK, one near Trat and me in Chiang Mai. Someone there might know, too.
*Rick