They have pretty much everything to do with baking and it is a virtual aladdin's cave of cooking stuff. It is like a cross between a pound (dollar) store and a cooking gadget emporium. They also carry all kinds of spices and ingredients I haven't seen elsewhere.
They have a web site: http://donaclara.com.ar/ but it doesn't show everything in terms of ingredients. I would be pretty sure they have green food colouring though.
(although I would never adulterate my Guinness when drowning the shamrock)
Here in Argentina, I have never seen liquid food coloring like we have in the states, but easily you can find the same kind that comes in a paste like we use for coloring icing in the states. That you can find in any costillon.