"On y trouve de tout"
Is a common oral use in France.
To understand de like the de following an indirect transitive verb is a mistake.
Let me give you some examples :
Au supermarché, on trouve :
de la viande
et enfin, des caissières souriantes
de is not related to the verb trouver construction, but to the property of the complement to be countable or not. fruits, yaourts, caissières are countable, in this case don't use de. lait, viande are not countable, then use de (like some in english : some milk, some meat)
Then how about anything? Is anything countable or not? That's a good question. French grammar says no, that's why we say de tout.