I've heard from many people that the wood the accordion's made of makes no difference in the sound of the accordion, it's all in how the reeds are tuned and possibly the wood block that the reed plates sit in.
I'd say be careful of what wood you choose, idealy it should be sturdy wood, whatever you decide.
There are sturdy light woods out there, I just don't know of any. I'm not very familiar with alot of wood. It seems alot of the lightest popular woods are about 7 or 8 pounds (I forget which) per accordion.
I was gonna prank call a builder and say that I want one made of "Charles wood." However, I don't think they'd find any humor in it though!