There are two women who sell tamales daily, from about noon on, in the parking lot of Comercial. They are on the north side, and both make excellent tamales. I'm sure you could arrange for them to have what you want when you want them, just by talking to them once you arrive.

The finest tamales in Zihua (IMHO)come from the second story of a house that sells dulces on Vicente Guerrero. From Benito Juarez, turn onto Ejido and go to the next street. That's Vicente Guerrero. Banamex is on the left corner closest to you. Park. Look for the wooden sign that says Dulces Tamales one door toward the beach on Vicente Guerrero. The first floor sells candy, sort of, and they will yell up to the lady upstairs. She'll come down and make arrangements with you. This is also across from the laundry that can be used as self-service.

In the Mercado, there is a small stand that always has tamales, too.

They are all very good. Keep it easy on yourself!