Accu mounts do them they are on fleabay look under lee enfield in militaria and hit world wide search you have to buy the 2 pad set that's the only thing
Try this link - Pads 4 LEE Enfield British 303 NO 4 Sniper Scope Mount | eBay
P.S the forumers here reckon Accumounts do a good job of the repro pads and the brackets you will have to get the screws as well Peter Laidlerwould be able to tell you the size/length and thread pitch