If you took the GED in the Avenal State Prison in California, you likely can get a copy of your GED through the California Department of Education. You can get duplicate records through ETS (Educational Testing Service).
ETS - GED Records Center
P. O. Box 4005
Concord, CA 94524-4005
If it's a different Avenal State Prison, let me know what state it's in, and I'll get you the contact information.
The GED Academy