Have you tried any of the bulk petfood stores? There's also the equestrian shops that sometimes sell bird food especially for pigeons. Useful as well for molasses in bulk, about ?5 a gallon.
In fact, seeing as Leeds has a good collection of pigeon fanciers ( the guys that dress their prize pigeons up in tights and say "Coo-coooh! Who's a pretty bird then? ) I would have thought many of their shops would sell hemp, certainly wheat. Try pigeon conditioner! Honest, its smells of aniseed and fish love it especially barbel.
