I'm in the UK so can't really help but I believe in the US complete mouse foods that are ok and can be ordered online include Harlan-Teklad (lab blocks) and Sunseed. I'm sure someone more local to you will be along to help. If you have access to a farm/equestrian shop near you and a car, then you can buy big sacks of 'straights' (grains), dog food and bird seed and make your own mix, IMHO definitely the best food (and probably the cheapest).