I've seen Mobil ATF 3309 at Canadian Tire locally in a 5 litre size. At $29.99 that is the cheapest I can find locally. This is simply rebranded as Toyota T-IV by Toyota. XOM is the only North American supplier of fully licenced T-IV/3309. The other supplier I know of is Idemitsu (their Type TLS).
The Mobil 3309 exists in large jugs. They are just extremely hard to find.