Although the immediate area of Los Tuxtlas is only the source for 3 of these humongous sculptures.
I include the subject here because:

1. they are colossally fascinating and
2. they are a great way to visit Veracruz and Tabasco and start your own collection.
References

Culture.com - Collect 'em all
Mayaglyphs - Olmec colossal heads as recarved thrones
jorge & memo - Cabezas colosales del mundo (all 17 on one page)

Photos
George And Audrey DeLange - the Museo de Xalapa heads
Xalapa Museum
.    
Xalapa Museum
  Tres Zapotes
Santiago Tuxtla
Santiago Tuxtla
 
Xalapa Museum
 
   
   
   
   
Archaeology of Los Tuxtlas

Head Hunters