This is obtainable early in the game
Mild spoiler ahead
After exiting the Ice cavern early in the game you will enter your first town called Dali. After a short cutscene with everyone going to sleep Zidane will wake up by himself. On the left hand side of the room is what appears to be a small desk fountain. Interact with it to get a fortune for 10 Gil.
There is no guarantee you will get a Very Good Omen immediately but you can constantly attempt until it pops.
If you don't want to waste money there is a Moogle in the reception you can save at and reload once you have got the fortune.