Well, I was going to recommend the S2W Airthru Stock from Special Ops but I just checked their website and it is no longer on it. I have one on my SP-1 and its the best. It basically screws into the bottom of the grip where the ASA is located. You removed the ASA and replaced the line with the macro line (included fittings and hose) I replaced the QD with a Proconnect III right out the bottom back of the stock where a remote works best(out of the way). The best thing about the stock is that it attaches under the grip and has an open area near the back top of the gun. This gap allows you to get your mask up tight to the gun while shouldering it. It is not fold-able but it's very light weight and balances my gun perfectly. You may be able to find one on ebay. They were about $80 brand new, and well worth it. Maybe you can call Special Ops up and see what's going on, they had a machinist making them up but he was only making them when they had enough orders.