Just search No Drill sling mount, one end will strap or belt to the stock and the other straps to the Barrel, I even DIY'd my own in part using a Dog collar and then a conventional clamp on the faux magazine tube on the RR.
They hold alright but arent perfect so check things are correct each time you take it out with the sling on.
You'll Shoot your eye out Kid
Currently looking for an SMK/BAM B4-4 Rear sight or help modifying current one.
Wanted Daisy Model 25 or Norica Commando in reasonable condition.