There are a lot of online sources for Guatemalan recipes. The recipe swap forum at Epicurious.com has a section of Guatemalan recipes. Whether they are authentic or “unique” to Guatemala, we don’t know, but it might be a good place to start.
Another is the Roman Catholic Maryknoll Mission, which evangelizes in Guatemala and around the world, and produced the Maryknoll International Cookbook , which includes Guatemalan recipes. Recipehound.com has a page of Guatemalan recipes. There are quite a few others, some in English, some in Spanish.