Since the plane is about 20 yrs old, I'm sure all canopies are long, long gone.
It's not a big size or complex shape. So one could carve/sand balsa blocks to fit to make a plug in the desired shape. Then cut a large plastic soda bottle, and use a heat gun, to form a canopy around the plug. Trim it up, and then mount like the original. Keep the plug if you ever have to make another. Or do the same with sheet plastic, in a clamping frame that has been heated in the oven, and then pulled down over the plug. For this size/shape no need for a vacuum former.
Or shape a block of styrofoam, and then use 1/16th sheet balsa glued on the outer surfaces. May take some piecing it together, or playing with getting it damp with ammonia to get it to bend around the corners. Sand and fill as needed, then use covering material (gray, black, whatever color you like). Glue the whole thing (foam and balsa) in place. The only hard part would be undersizing the styrofoam to accommodate the thickness of the balsa sheet, if you want it to be flush on the sides. But having the balsa overlap would be fine, just like the original plastic canopy, and easier to build too.
Or do the styrofoarm shape, and then cover it with fiberglass and epoxy instead of balsa....
There's a bit more to each method, but it's not hard to do. Some searching through the build threads for "how tos" should give lots more info. Any will be far cheaper than a premade canopy you might possibly find.