I've looked around a little, and I wonder if we couldn't use something like the a model aircraft canopy from Park Flyer Plastics. I'm looking at the Aurora, which is 11" x 3 1/4" x 3"; it might be cut to the size and shape needed.
At $6 (plus $2 postage), it's probably worth a try. They have 99 different canopies, plus other pieces that might work well (engine nacelles, drop tanks, etc.). Here's the link to the page containing the Aurora information:
http://parkflyerplastics.com/cart/index.php?main_page=index&cPath=46&sort=20a&page=4.
[EDIT]: There's another model that looks even better: the Geobat 28 inch. It's 6-1/2" long X 3-3/4" wide X 2" tall, and costs only $3:
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I'll admit that the Sky Raider unit is the best I've seen. I'd love to have its clone.