The easiest way to get a nice Stormtrooper blaster is to purchase the Kenner toy, shown below. While this toy is not accurate, it is inexpensive and lightweight. You can simply prime and painted, but you can remove the LED and sound and add doo-dads to the outside to make it a little more realistic. Krylon Ultra-Flat Black gives a great finish. Check out this site for specific information on how to make this toy look more accurate.

Other options include: buying a resin kit, building one from PVC or converting a real Sterling sub-machine gun. Of course, you can always custom make your own! Keep in mind, any metal replica will weigh several pounds. This can make it a little heavy to hold for several hours at a convention.

Visit these sites for more information on Stormtrooper blasters: