"I will have it for you."
Translation:Lo tendré para usted.
It doesn't work, beacause "te" and "se" works as either Direct (accusative function) or Indirect Object (Dative function) in spanish, in a very strict way. They just subtitute teh prepositional phrases which include "a" (as "a mi hermana", "a su camello, "a ti"). So, there are two reasons why it's not correct:
You cannot "have something to someone". Thay same way, you cannot "tener algo a alguien". So, tener, simply, doesn't accept "te" with a dative function in Spanish.
Deeper reason: "For" in this case, correctly translated as "para" in Spanish, serves here for showing the "destinator" of something, that is not the "second receiver of the action", as dative case means.
Explanation of the "exceptions": A. Although it could work, as it works with the verb "dar": "Se lo daré/Te lo daré". But in "dar" the "gift" connotation is in the verb, not in the grammar. It's clearer if I use a, for example, "decir" (to say). "Te lo diré". "I" am, simply, the second receiver of the verb "to say". B. But, anyway, some verbs, could be used that way, as "hacer" ("to make/do"). But it is because, the verb itself can use "a" and "para" as prepositions. So, I DO can say "Te lo haré". But just if you don't use the "gift" connotation. For example: "Te haré lo que quieras (I will do whatever you want to you)" = "Te lo haré". But "Haré un regalo para ti" = "Lo haré para ti" but NOT "Te lo haré".
Anyway, sometime, due to mistakes using the language or whatever, you could hear those things. In fact, I doubted when I first read this comment if it was right or wrong. I think that, in the end, it depends on the verb your are using and what are you using that verb for expresing for. In this case, tener simplay cannot be used that way (tener/hacer/haber/ser/estar/... all of them are weirdos xD).