I usually buy my organic stuff from the Tongyi Youji (Uni-President Organic Foods) and Li-Ren, but that's mostly because those are my only two options down here.
However, my father-in-law frequently chastises me for this and tells me I'm wasting my money. "Taiwan doesn't have an environment for organic food" Well, he said that in Taiwanese, but his meaning was that no food grown in Taiwan could really be "organic" and so I was wasting my money. Money I should be spending on his beloved daughter and grandchildren. Now, I'm not really sure what to believe. Certainly the recent news about dozens of different kinds of pesticides being found in supermarket fruits and vegetables would give anyone pause. Even when I buy non-organic, I usually prefer to buy from the local open-air markets. Somehow it feels safer, although that's probably just what I tell myself.
As an aside, I often get the feeling these days that a large group of people are trying to poison us - what with the ractopamine, plasticiziers, pesticides, and whatnot. Who are we to trust?