That guitar is amazingly cool. I love the shape of the body. You were probably told it was a Regal or Harmony because by the late 1930s they were about the only companies with them in regular production. The only other possibilities might be something like Oscar Schmidt which, although dropping 12 strings from the catalog in the mid-1930s, still made them as special orders or the small shops like, as mentioned, Holzaphel.
Bottom line though is any 12 string made in the 1930s or 1940s is one heck of a rare find these days.
