There are front sling swivels available commercially that fit the 30-30 Win but not sure how they would fit on a 357 tube. They are a simple "pinch the tube" bolt on item.
Other than that I have used a piece of latigo leather/heavy leather boot lace stitched to a sling swivel around the barrel& tube and it works sufficiently for the job...it will slide a bit on the barrel but still works.