"I find you a smart person"

This sentence could have two meanings depending on context. It could mean the same thing as "I find you to be a smart person." If you want this meaning, than either phrase would be fine. The only difference is that you are implying the "to be a" of the sentence.

The second potential meaning is that you are going to seek out a smart person to then give to whoever you are talking to. (Hopefully that makes sense.) If that is what you are intending on saying then you would phrase it like this. "I will find you a smart person."

"I find you to be a smart person" is the full correct sentence

"I find you a smart person" you will hear this spoken colloquially, it means the same it is the shortened version of the other sentence. But it sounds a lot like a non native speaker making a mistake with this sentence.

"I will find you a smart person"

"I will find you something to eat" [parent to a hungry child crying and asking for food in a public place] the parent is saying I will get you some food somehow somewhere.

A non native might say "I find you food" are they saying "I find your food" with a mistake on the pronoun or "I will find your food" or "I will find you some food" "I will find you some food" removes any uncertainty. now we know what the parent is promising to do.

You will receive answers saying there is no grammatical difference, but there is some potential confusion as to what the sentence sentence is saying, without the "I will" plus the determiner "some" some food