Oklahoma City Gun Club (in Arcadia) has a bi monthly steel challenge match on the 3rd Saturday of the Month. Next one is in February.
http://ipsc.okcgunclub.org/steel_challenge.html
United States Shooting Academy in Tulsa has a match the 1st Sunday of the month.
http://www.usshootingacademy.com/content.aspx?id=102
I've shot both and both are well run.
Looks like the Ponca City Rifle and Pistol Club shoot on the last Saturday of the month.
http://poncarpc.org/
Every Steel challenge I've been too has welcomed Rimfire and Centerfire shooters.
You might also want to check out the state firearm websites.
Oklahoma Shooters Association has a competition section.
http://www.okshooters.com/forum.php
Boomer Shooters is primarily a Oklahoma shooting competition website.
http://www.boomershooter.com/
Brad