There's a little place around here that sells it. I guess you'll have to check around your area. Don't know what kind of place would sell it. Maybe someone here will chime in. I know Razor buys his at the track but he goes quite a bit. I buy it 5 gallons at a time and mix it in my reservoir with distilled water. It lasts for months.
Actually, mixing it with water is supposed to make it much less corrosive. I haven't had any kind of problems so far and haven't seen any signs of corrosion.