I found it everywhere for my 1 year old. Never had a problem. If you have a room fridge, get a few chugs at your hotel. If you don't have a fridge, most Disney hotels will put one in your room at no charge. Tell them it is for your baby.
Worst come, you can always have milk delivered with whatever else you need from an online grocer. We ordered all the toddler supplies, diapers, baby food, yogurt, cereal, etc with a case of water. We have used garden grocer.com, they deliver in the morning. Bell services kept everything cold until we checked in after 4pm. Much better then trying to pack diapers, etc and keep the suitcases under the airline weight limit. I even had the "snack pack" sent to our room from the Disney Florist (.com) which includes a cute little insulated padded cooler for formula/milk. Our youngest was 2 months at the time. Garden grocer was a huge help then (2007).
Hope this helps.