Hi, here is a link to a DIY wooden air stone. He uses Basswood. I have seen Basswood at Michael's (a craft place) in Edmonton.
http://www.hawkfish.org/snailman/kwairstone.htm
I would just cut the Basswood to size and drill it most of the way through, and glue a short piece of rigid airline tubing to it. Remember that the air only comes out of the sides with the grain open.
Hope this helps.
Dave