axle50,
I know the wood pieces that you are talking about, but have no idea where you can get replacements. I have a Canadian 40 Chev as well. I haven't seen the bottom of a cab on a US 40 so can't tell you if they are only on Canadian trucks.
Here are a couple of pictures of the wood blocks that are still installed on my truck.
Pics of wood blocks behind rockers They are rotted as well, so if you find a source, I would be interested in hearing about it as well.
