Are you looking for a muzzle protector, their pretty easy to come by. I bought one from a guns shop that was basicly a brass cone that works for verything for me from 6.5mm to .50.

If you take an empty brass case of .264 caliber or smaller -a .25-06 case would probably work really well, and cut the neck portion off about 3/4" back from the mouth of the case and chamfer the brass edges, you should have a satisfactory bore guide.