When you say redo the deck, what exactly are you planning to do? Foam can be had from many place such as your local Fabric type store or 1 of many online places. If by redoing the deck you are talking about removing the existing floor and replacing with new plywood and the glassing in. Those supplys you can get at different places.
I do have to redo the floor, so I know where to get the wood, it's the foam and fiberglass resin type of stuff that I'm looking for, what kind of foam would I get from the fabric store?