promag makes a 30 round mag, but they are usually backordered, you have to do some websurfing to find them, but you can look at it at the promag website. good product just not practical, most of the people i know who have picked one up used it once or twice and that was it. you cannot carry one in the weapon because it sticks out too far. i carry a modified mag in my XD9, i carry 24 rounds, 6 mags times 24 rounds in each, thats a good carry load.
I can't imagine what you would need more than the regular 16 round magainze for the XD9... I'm pretty sure the 45 carry's 13?
If you're at a public range, most of them have a 4 or 5 round limit anyways so that high mag shooters aren't hogging the range.
If you want them for the range, just pickup a bunch of extra magazines and a speedloader. For my XD9 Service, I had 5 16 round mags and 2 10's... It was more than enough for any day at the range when you took breaks inbetween to speedload.