Try looking on the USTPA website, or try a general search on Google for Team Penning clubs in your area. You might also try AQHA they have quite a few pennings and sortings. Jared Lesh from OK does clinics but I am not for sure where or when. He does have a website just search for Jared Lesh. Enjoy it is a ton of fun.
The Lesh brothers are amazing penners and do lots of clinics all over. I did a mini clinic with Joel Lesh and found him very helpful and positive. He also really pushed me. Another great clinician is Phil Mainey out of Montana who also has clinics all over. I have never actually rode with him but purchased a horse from him. Again super knowledgeable, positive person to learn from. He has stayed in touch and answers any questions I have, and I am just a "newby" to the sport. Find local penning associations in your area, most have websites. They typically post clinics available. Learn from the best you have a chance to learn from.