Man i love my gamo.When i first got it i had to get use to it but once i did the groups got tighter and it settled down alot.
What you have to do is to get some sling studs and then once you have those you take a drill and drill into the part of the stock you want your sling at(just make sure that the stock is not thin in the area you are drilling).Next you screw the studs into the drilled holes.now the fun part,you pick out you a sling that is compatible with this setup.btw you can also attach a bipod to the stud on the forearm.And there ya go. ;-)