I know my Shoot Boss box has gotten low on these after I've sold/given away/lost my stash. This is a good deal...$6.99 for a set of Uncle Mikes
http://www.midwayusa.com/product/774577/uncle-mikes-quick-detachable-super-sling-swivel-set
If you are a new customer they have a 15% promotional code to look for : $5 off $25 order / $15 off $100 order.
(this won't count toward the swivels as they are on sale, but if there is something else you need to add to your order)