You might be able to get the Esbilac at Petsmart or possibly Walmart:
#5) WHAT TO FEED (FORMULA):
NEVER, NEVER, NEVER, FEED COW'S MILK, WHIPPING CREAM, WALMART FORMULA BRANDS, EVAPORATED MILK OR HUMAN INFANT FORMULA TO A SQUIRREL!
These contain WAY too much lactose for squirrels, and have only a 4% to 6% fat content. Squirrels require 30% to 40% fat content in their diet!
The ABSOLUTE BEST choices of formula for infant squirrels are Esbilac or GOAT’S MILK ESBILAC. These are puppy’s milk replacers, and closely resemble the components of a flying squirrel's mother's milk. They are made by Pet-Ag and available at Pets-Mart, PetCo and Tractor Supply. Some Vet offices keep a supply on hand. UPCO usually has the best price if you order online www.upco.com or phone/mail order at (800) 254-8726. 1- 12 oz can of the powder should be enough to raise 1 squirrel to weaning age. The mixing ratio is 3 to 1; 1 part formula powder to 3 parts water. Formula is only good for 72 hours after it is reconstituted or mixed, then the vitamin and minerals will begin to evaporate, so mix small amounts accordingly. The Goat Milk Esbilac is made of a goat milk base, and does not bloat, constipate or cause diarrhea.