If you search google for "autos usados Panama" several sites will come up and I'm not sure which one has the most vehicles. David aka Tapage here on Mud would be a perfect person to ask as he lives in Panama.
New Toyotas in Panama
http://www.toyotarp.com/mapa.htm
a few used cars
http://www.encuentra24.com/clasifica...ma-316-en.html