J. J. Perodeau sleeves double rifles. I handled a .500 Nitro that he had sleeved to the original caliber and it was gorgeous work. Yes, this involves the use of the rump of the original barrels as a mono-bloc. He also makes new chopper-lump barrels to the original profile. His web-site says $3,000 up for sleeving. New barrels are $7,500 up.

I don't know of anyone offering a re-lining option (cleaning up the chamber and bore and inserting a tube) but I imagine someone, somewhere probably does.

The problem with double rifles like this that really need new barrels is that it is hard to put them back into service condition without finding yourself upside-down.With sleeved barrels, it will never be worth as much as it would be with original barrels in usable condition. With new barrels, it will never be worth as much as it would be with original barrels in good condition. The price needs to reflect this and, these days, rarely does. A hammerless Holland Royal in .500 Nitro in the condition that you describe would still be worth some bucks and probably worth re-barreling. A Holland LOG (lever over guard) BP hammer gun in such condition needs to be priced at "give it a bowl of milk and it will follow you home".
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