You can shoot your gun & holster combo in the IDPA class in Steel Challenge.
SC matches, in my experience, let you get in more shooting than IDPA in the same amount of time and the matches go faster because there's no target pasting, no scoring rings on the targets and no walk-through for each stage.
Plus there's the wonderful instant feedback when you hit the target, paint flies and you hear the target ring.
Or you miss and dirt flies.
You'll never be a fast as Doug Koenig (see below) but you'll have just as much fun.