I think the other option is Barretta mags...Kalrog wrote:
If you get the one that takes the Glock mags - yes they do. If I remember correctly, they can either be set up to take Glock or Ruger mags... might be something other than Ruger though...
I used a 33 rounder in my Glock 19 once. Kind of hard to conceal :) but great for the range.