Your sentence is wrong. You need to conjugate the verb:

On trouve tout

When talking about a place (like Reims), it is referenced by the “y”:

On y trouve tout

“De tout” is used to say that you find “of everything” or “of all”, not “everything” per se. So we add the “de”. Otherwise, it would imply that you can literally find everything there.

Other example:

Il est capable de tout (faire). (He is capable of anything)

Loin de tout (Far away (from everything))

De tout mon coeur (with all my heart)

Trouver is transitive with a direct object. « Trouver de » is not a construction in itself, however de is commonly used as a partitive article after some verbs. In “trouver de l’argent”, de l’argent (some money) is a direct complement built with the partitive article.

Tout is a pronoun which like a few other pronouns (ce, ceci, cela, ça, quelque chose, rien, others?) can be used with a partitive article. This explains the use of de tout (a bit of everything) in your sentence.

The meaning of “de tout” is very close to “toutes sortes de choses” (all sorts of things, as mentioned by BBBreiz). Without the partitive, as in “On y trouve tout”, the meaning would be plainly and simply “everything”.

You might also say:
“On peut y trouver de tout”
(“de tout” means “all sorts of things” meanwhile “tout” means “everything“.

“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 :
des fruits,
des yaourts,
du lait,
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.