It's hard to find a Duo with the shutter linkage intact. FYI, they're a 6x4.5 format.
Originally Posted by verney
The Medalist would be the top choice; they routinely sell for $150-250. They're also very heavy. The Kodak Monitor with the 4-element Anastigmat Special lens would be more economical, and its Supermatic shutter is reliable and fairly easy to CLA. This lens/shutter can very occasionally be found on the Kodak Vigilant too.
The Tourist with the top-of-the-line Anastar lens has the Synchro 800 shutter, which is touchy and appararently unrepairable by the average human. Tourists equipped with the Anastar also have a serial # on the lens. They do give very good results for a 60-year old kit: