Google for tower hobbies, hobby lobby, hobby people. If you're into fabricating from scratch, buy bulk foam and a hot wire cutter. Hot wire the foam into rough shape, sand it to final shape, then fiberglass over it. Embed carbon fiber if you only want to use a very thin/light fiberglass shell. If you want strength and don't mind a little extra weight, have the fiberglass stick to the foam and carve out room for the guts. If you need more room, put a releasing agent (gel stuff) on the foam before glassing over it, and then the foam core just pops out leaving a fiberglass shell. To do it really well, you'll want to vacuum bag your composite layups especially if you use multiple layers of composites (like fiberglass over carbon fiber) to prevent delamination.
There are other plastics you can mold. Many people will carve stuff (like canopies) out of wood, and then melt a sheet of plastic over it in an oven (don't use wife's oven, buy a cheapo one and put it in the garage).
All of that stuff should be available at the R/C hobby stores online. If you need help or larger equipment, you might also consider going to a car modification shop (the kind that turn $13,000 hondas into $30,000 pieces of $h17) because they may have a skilled fiberglass guy and might let you use their shop for a small fee. Vacuum ovens for curing composites are expensive, but you won't need one of those unless you get really exotic.
