CX4 .40 S&W high capacity magazines

I recently purchased a Beretta CX4, .40 S&W and I'm trying to find high capacity magazines for it. So far the largest I've found was 17 rounds. Does anyone know if there's a bigger one available and where I can purchase it? Ideally I'd like a 30 round magazine, but I'd settle for 20 if I must (and if I have to settle for 17, I imagine I won't have much choice then...).
On a side note: how the hell do you use the search function on this thing?
Thanks,
Rich