I didn't have time right now, but another approach would be to use this list of engineering blogs[2] and scrape each one for mentions of "elm" "elm lang" "elm architecture" etc.
Sources: [0] https://github.com/jah2488/elm-companies [1] https://pastebin.com/2FY5fTS1 [2] https://github.com/jah2488/elm-companies