They don't make magazine carriers for the SR45 right at the moment but you might want to check out http://www.kytexgear.com/. Shoot Brian an Email and find out if they will be making them for the SR45. I've bought carriers from him for both my SR9c and LC9 and they are great!
You can get paddle style adjustable dual mag holders at CDNN for cheap. Great for my needs in IDPA and I have double stack and single stack versions. They use to be 6.99 each.