I used to be a frequent contributor on Concertina.net, and the de facto Chemnitzer/LSGC* "expert".
I now only visit occasionally. Send me a direct message through the board or reach me on twitter (@oakblood3) if something Chemnitzer-related comes up and I'll join the thread.
You could also contact me through the form on my Cicero Concertina Circle website, but please: Do not email photos without asking first, and do not ask for appraisals of value on any instrument. Do not ask me to help you sell your concertina, and I am not in the market right now to buy it myself.
*LSGC: "Large Square German Concertina". I think this term was coined by DoN Nichols on the rec.music.makers.squeezebox usenet group.