Hi dude,
Best shot is finding a sympathetic petshop who breed their own. Consistency of suppy is a bugbear though. You could always breed your own though butif you do be aware mice stink. Search on google or somewhere for fancy mice breeders - they tend to have a lot of babies that dont make their exacting spcifications that they sell of cheap as pets.
Life is a lot simpler if you can get them eating f/k though as you can have those shipped from quality mail order companies etc.
dr del