If you plan on using hair conditioner while traveling in Guatemala, you'll want to bring your own. Hair conditioner the way most westerners are used to it is near impossible to find in Guatemala. The closest thing to hair conditioner is what westerners would recognize as leave in conditioner (often referred to as crema para pelo), which is used in Guatemala both for styling and conditioning hair. Normal wash-out hair conditioner is not available for purchase throughout most of the country, although it is available at malls and styling salons in bigger cities like Guatemala City or Xela (Quetzaltenango).
Various forms of activated styling cream are widely used and available at just about every corner store (tienda) in bottles or single serving Q1 ($0.13) packets, pictured above. These creams protect and condition hair but are not meant to be washed out, and they're sold in even the most remote regions.
If you'd prefer regular wash out hair conditioner, you'll probably want to bring some with you to Guatemala..