NAPA stores have it. Maybe Car Quest too.
You need a Ford approved G-05 coolant. Stay away from the universal (AKA Dexcool w/o the Dexcool name) crap. NAPA stores usually carry Zerex G-05, but you will have a hard time finding it anywhere else.
Zerex is usually $15/gal or so. Motorcraft is usually around $17/gal, but it depends on the dealer.