There is a shop on Corrientes in between Montevideo and Rodriguez Pena called El Gato that has a whole wall of herbs and spices. I did see various curry powders if you're interested in making your own paste. From memory they were more Indian that Eastern Asian. I'm not sure if this place is a chain, I only know the one there.
I don't think its very cheap but if it stocks what you're looking for..... so be it. I bought cocoa there for $2.25 for 25g and then later bought it in my barrio at a dietica for $4 for 1/4kg.