Buy it from the track. Regardless of how it’s sold, you’ll need your own plastic jug for mixing the oil with the fuel and for storing mixed fuel. If you haven’t already, get a Ratio-Rite or similar mixing cup to make dispensing the right amount of oil a snap.
Last time I was at Centennial, they were only selling 5-gallon jugs (you’ll need VP93 for your Rotax). The jug was 50-ish bucks, but that was last month… 😯