This page of our guide to Psychonauts 2 lists the Memory Vaults available in Compton's Cookoff.
There is only a single Memory Vault found in this level.
Ford & Lucy's First Date
Location: Downtown Center.
You'll find that secret right behind the billboard. All you have to do is ride behind it, knock down some bowling pins and jump off the ball. That's where you'll find the Memory Vaults.