as a Maccann-Player, I know exactly what you mean. It took me 3 years of playing all on my own until I heard another concertina player live (I had to go to Ireland and took some Anglo lessons!).
I´m afraid I can´t really help you. The only thing I can think of are the instruction manuals on the concertina.com site http://www.concertina.com/maccann-duet/index.htm But these have not been very helpful to me, because the musical style is just not where I want to go.
The arrangements of David Cornell were helpful though, because he writes out the fingering. It was interesting to learn how his fingers move.
I know how frustrating it can be, not to have someone to guide you through the learning, but it also has it´s advantages. You HAVE to develop your own style of playing and you will. Sometimes it is refreshing to me, to see the concertina as the little box with these knobs, that waits for you to bring it to live. I see it as a little organ that has so many possibilities. It only depends on your imagination.
And sometimes it can be good to limit yourself. Maybe you could set a smaller aim? For example - be good in certain key that suits your singing.
I don´t think that I could teach anyone anything on the concertina, but if you are interested, we could maybe setup a skype connection or something, could be interesting.
And: through the years, I tought myself a few instruments, but always only to a certain degree. At some point, I kind of lost interest. A few years ago, I read a post on the internet about becoming frustrated with an instrument. It said that if you become frustrated you should analyze why. That was good advice. It´s always good to remember why you play an instrument anyway and it always should be fun.