Sustainable Industries magazine had a great article in their Sept-Oct issue. It reported that when asked where Trader Joe's gets their organic produce, Joe wouldn't answer!
Some grocers will share this information. Others won't, citing concerns about competition and needing to protect sources. Many grocers then allow a third party to authenticate that milk really is organic or eggs really are cage-free. Trader Joe's does not have third party authentication.
Please know, I am not maligning Trader Joe's. I think we all have a responsibility to make choices about what we ingest and can only do that when we have appropriate information. If a grocer won't provide the information and isn't being responsible about providing authentication...well how do you know what you're getting?
I've been to several stores which sell both conventional and organic produce. I've seen stock clerks take conventional produce, mistakenly placed in an organic bin, and move it. By law this would render the entire organic bin "spoiled" but of course no retailer can afford that kind of loss.
If you are fortunate to live in a place where you can buy directly from farmers that's the best. You can talk to them and find out their practices as well as buy very fresh food. If you have the option to buy from a store which only carries organic food, that's a no-brainer.
Question from where your food comes. Read labels. Make choices about what you ingest.