Vegetable dye can be found at some dietica shops. I spent an entire day searching. I've been to about 6 cotilion in V.del Parque, 4 pharmacies, 4 bakeries, even some art supply stores... nothing.
Finally, a dietica on Nazca had red, blue, and yellow in 30 cc bottles, a brand called Fleibor.
on the bottle:
Laboratorio Fleibor SRL, 30 de Agosto 162 - Tablada, phone 4652-8035