"...what I need to do to prepare to this..." Join a club that shoots NRA or ISSF(used to be ISU shooting.) matches. Preferably in one of the leagues Tim mentioned. They're usually scheduled matches between local clubs. Great fun. Other than that, you really don't need to do anything to prepare.
Yes, there are .22 only matches. Customization nor 'dot' sights are required.(real men stand on their hind legs and shoot with iron sights) Reliable ammo that shoots well in your pistol is.
As to where, look at Losangeles' link and contact your local NRA office.
You have their url. Here's the ISSF page.
http://www.issf-shooting.org/
Have a look here too. Relax though, it's clubs affiliated with the U.S. Olympic team. Look at it as a place to shoot and don't worry about the Olympics. At least not right away.
http://www.usashooting.com/index.php