A local gunshop would likely be the easiest but I am not familar with your area. Barring that Brownells has dovetail slot filler blanks and filler screws. I usually make the slot fillers from broken sights in the junk drawer and some junk lots I've bought on EBay. The fillers screws usually accumulate around here from receiver plugs removed when mounting scopes although I think I do have an assortment around here somewhere..