This is only one of three ways that I setup my two point sling on my A2 rifle, Blue Force Gear A2 buttstock adapter.
I've got three ways that I'm mounting my two point slings on my A2 clone rifle, the first way is the simplest, I just use paracords and use IDF Israeli style two point sling, they're wide, comfortable and easy to mount. There are many sellers of the IDF slings at e-Bay.
My second setup to be retro 1980s era is I use a USGI USMC Marine type sling with a metal clip at the back end, it just slips on the sling mount of the A2 fixed buttstock.
And my third way is I use the Blue Force Gear A2 buttstock adapter in the pic part number A2B- (link below).
With the noted Blue Force Gear A2 buttstock adapter you could use any kind of two point tactical or USGI slings.
http://www.blueforcegear.com/a2-buttstock-adapter.html
USGI two point sling source:
http://www.cjweapons.com/aspcart45/default.asp?page=299&start=1