I haven't seen any for sale, it might be worth giving Steve Pope or Airmasters a call, they might have some kicking around in their spares boxes ..
Otherwise I think you could probably get some mounts and have them engraved. I think you would have to get steel mounts rather than alloy, so perhaps put an advert up for them as well. The custom motorcycle people and obviously the posh shotgun people are keen on engraving, you might be able to find a reasonable craftsman in one of their mags or websites.
Good luck!