In chile you'll find Avgas in nearlly all big Airports and Airfields used by Flying clubs.
That's... Arica, Iquique, Antofagasta, Copiapo, Viņa del Mar, Santiago, Curico, Chillan, Concepcion, Temuco, Valdivia (SCVL), Osorno, Puerton Montt (and by that city im sure you'll have already start your trip to argentina) but probably many more places, i'll leave here the AIP Web Address anyway
http://www.aipchile.cl/dasa/aip_chil...AD%20Parte%203