There are some good tutor books about. I have one by Bertram Levy called 'The Ango Concertina demystified'. I got it from the Music Box in Cleckeheaton when it was still Mally's Melodeons. Comes complete with 2 cassette tapes and seems to be pretty good. You do need a 30 button C/G though to get the best out of it though.

Cheers

DtG