Does anyone know of a source for Plainchant music transcribed for Bb clarinet.

Thanks

I don't know of anything like this but, if you want to play it by yourself, you can just read any music as it is. However if playing with other people you have to transpose the music up a tone (ie if written in C you play it in D). This is a very useful thing to practice - doing it with plainchant would be a good introduction to the skill as the music is quite simple. Don't even bother to write it out just do it at sight.