But doesn't Quito have good coffee, too?
Anyway, you could always grab the van to either of the Hampton's which is about 5 minutes from the airport, walk toward the chicken place, then past it, until you find a colmado or store. Grab a taxi back, or return as you came.
Or just grab a taxi and 'coffee hunt.' Work a deal w the cabbie for say 1 hour.
Facil. No problema!