This site has a really cool listing, with pictures, of double hose regulators. I like that there is a rating system (1-5 stars) depicting the rarity of each double hose regulator they list.
Among the rarest is a “blue can” Mistral made around 1958. I own one that is original and still working (You can see the label here: http://www.vintagescubasupply.com/labsusd.html). I’d love to know more about it. I do know that the same regulator was once sold by Sears under the J. C. Higgins label, and saw a picture of one once that had the Mistral label affixed over the J. C. Higgins one. I’m not about to peel the label on mine to find out if there’s a Higgins label there too.
If you know anything about this regulator, please drop me a note.