I have found one local butcher who sells lamb rib bones and beef marrow bones in trays for 99p for about 3 huge chunks of marrow bone or about 8 rib bones!! A great find. You can buy them with the food from Natural Instinct, but at £1.50 each I'd rather not. Probably best to trail around local butchers and make friends - I always buy something else there as well for goodwill. Hope you find some.