This is the best place to get the plans on how to build a zapper and also the best place to have them build one for you. They charge $10 including parts, service, and shipping in US. http://zapperplans.com/>
Also, don't be confused a zapper is just any posativly offset frequency with anywhere fom 5 to 10 volts on it. Read dr. Hulda Clark 's book, zapping bugs.