Don't think so..
HK only makes 10 rd mags for the SL8 from what i've seen. As you know the receiver of the rifle is a modified G36 receiver that can only take the low-cap magazines. From what I understand the bolt carrier can only pull from single stack magazines as well. So even if you get a G36 magwell and magazine and modify the receiver, you still need the G36 bolt to be able to pull ammo from a double stack magazine. I've seen conversion kits out there but they ain't cheap. Any you still have a rifle with a goofy looking thumbhole stock. I bought an SL8 with some intensions of making it look like a G36, but it is too much work/money. Mostly just gathers dust these days.