As I've been saving up for a C-system chromatic button accordion, I've also been looking for hints on technique so I can figure the dang thing out once I have it. Here's a bit of info for anyone doing the same.
This page clarifies that confusing-looking wall of buttons:http://www.thecipher.com/chromatic-acco ... ipher.html
Here are a couple of videos of a CBA in action:http://www.freebidou.com/voirecouter_videos.htm
I gather that the right hand method in the above videos is a bit modern; in most photos of '30's accordionists that I've seen, they keep the thumb on the edge of the instrument and only use their fingers on the keyboard.
Hope that helps the curious. Please follow up if you have any more info on these beastly but wonderful instruments.