It's very lightweight fiberglass cloth. Try an auto parts store or r/c hobby shop. For the resin, use plain old fiberglass (polyester) resin or better yet, get some 15 or 30minute epoxy from the same r/c hobby shop. The long working time will let you work the bubbles out before it sets up. I laminated sheets of blue foam together with a spray adhesive from a hobby shop.
Cut the fiberglass cloth into small, manageable strips.
Hey- since it's all scratchbuilt, go bananas and do it in 1/8