You can purchase Far Cry 5 on the PlayStation Store. Uplay is a digital distribution service like Steam, Battle.net, Microsoft Store and the Epic Games Store; it's only on PC. As of today, Far Cry 5 is currently on sale in the PlayStation Store; it's 75% off like Steam and Uplay.
If you want to buy a physical copy of Far Cry 5, then check retailers such as Best Buy, GameStop and Target. It's also on Amazon.