inherited a Burgo 45 air gun. I was checking it out and loosened the front sight barrel and the insert fell into the grass, never to be found. I am wondering if I can just buy a single insert somewhere, rather than what I see are sets with 6 different sights for about $35.00. Second question, the dovetail on the top measures 1/2 inch. I see a lot of 3/8 and 11 mm rings but not sure they fit this Dovetail. Can someone clarify what size rings are needed to fit this gun? I am guessing this gun is 60+ years old as my uncle had it when I was a little kid, then passed it on to me recently. It still shoots great.