Guatemala City has been the only airport where you could get Avgas in Guatemala. Recently Avgas was added to the Mundo Maya Airport (MGMM). Since Mundo Maya is also an international airport, this makes it a great option to enter Guatemala when coming from the north.
Remember there are landing fees for N-registered aircrafts of 150 GTQ and some additional fees for another 30 GTQ or so. If you land at night, they will charge for turning on the light.
Great news for Guatemala Aviation.
Make sure to show you Aeroclub Guatemala membership to get a discounted rate.