It's been some time since I first heard that Epps had GP11 in stock... IIRC it was selling for about $30 for a brick of 60 or 80 rounds. They do carry all sorts of surplus mmo though and would be worth contacting.
In the US, it appears as though Grafs and one or two Eastern European producers like Wolf or PriviPartizan have produced ammo for commercial consumption.
After purchasing my K31 several months ago, I got 100 cases of Grafs from BCredneck.com and just loaded them up with regular 30 cal soft-points. I've since gotten an M96/11 as well at a great price and don't mind having to reload for such well built rifles. They almost beg the shooter to take their time firing and to do their best to take full advantage of the accuracy that they offer!
Best of luck!
Frank