Where do I get a subpoena? How is a subpoena served?

The Clerk of Court issues subpoenas.

A subpoena may be served by a sheriff, by his deputy, or by another person not less than 18 years of age. Subpoenas may also be served by registered or certified mail or statutory overnight delivery, and the return receipt constitutes proof of service. O.C.G.A. 24-10-23.