Pretty much anybody can act as a referee, so long as they are seen to be a responsible person capable of giving a reasonable reference. I'd go with someone without a criminal record, who is in gainful employment and you're pretty much there really. A nurse, a vet, shop manager, gamekeeper, teacher, garage proprietor, a supervisor at the local factory and so on. They can be retired too. Perhaps someone you know through shooting. I'm pretty sure that the vast majority of people would be able to find a couple of referees without too much trouble if you put your mind to it.