If any transcription has been made in the past seventy years or so, it's unlikely that you're going to find it for gratis, even in the days of the internet. I'd just go with the original music and transpose from concert pitch if I were you. Transposition, while a bit of a chore at first, is an excellent musical skill to develop, and it become second nature once you get "into the groove" of things.
As an alternate approach, if your piano player is facile with transposition, you could play the part at pitch on the clarinet, and have s/he do the mental scrambling.