I think that what you are asking is really an impossibility. Even if you can identify some brands you would like to support, products carrying the name may or may not have been produced by that same company. Look at the fine print on the packages and see how many products have “distributed by” or “produced for” on the labels. There is no easy way to tell where they came from.
Do you extend or deny your support by considering everybody who may have handled the product in the distribution chain? You have wholesalers, brokers, importers, transportation workers, ad agencies, and on and on, who together bring the products to your grocer’s shelves. The more people involved, the grayer it becomes.
Also, in a world economy, what may be deplorable working conditions to us may well be the means of survival for those in other countries. Working for subsistence wages may barely keep the wolf from the door and may rightly be considered immoral here, but it’s certainly a step up from scrounging for food scraps in the garbage dump in the only world that some people know. Your purchase of something produced in bad (to us) working conditions just may afford those workers and their families an opportunity to eat tonight.
Even shopping at the farmers markets and roadside stands is no guarantee that everything is as it should be. Most farmers use migrant workers at one time or another during the year. Some treat them very well, some don’t, and it’s unlikely that you would be able to find out which is which.
I do try to avoid companies that openly support causes to which the Church is opposed, Kraft and P&G being two which come to mind. A lot of small companies are producing private label products at much lower prices and, while I know nothing of their labor practices, I’d rather support them than the big boys, and hope that part of my dollar is going to someone who has earned it and who needs it.
Good luck in your quest, but I really think that you’re jousting with windmills.