My local Jewel Food Store sells goat's milk - situated at Howard & Kedzie, the SW corner of Evanston. I've seen the milk in the quart and half-gallon size, but not in a full gallon. The larger of the Devon Avenue Indo-Pak grocery stores probably have it also. A call to Patel Bros. on Devon Ave. will probably get you an answer.
Jewel Food Stores
, Elgin, IL 60120