The idea behind buying used clothing is to avoid buying new non-organic cotton. It's the same idea as just treating my clothes as well as I can so they last longer. The more use you get out of old clothes, even if they were created with pesticides, the less new clothes and pesticides are supported and purchased. A lot of used clothes don't get bought, they just end up being trashed or recycled. I figure if I buy a used shirt, that's one less new item I'll be buying and supporting.
I don't know any great sources of info off hand; but you could try a google search. The statistics, if I recall correctly are:
--Cotton is the number 1 pesticide-using crop in this country. It's also typically a GMO (Genetically Modified Organism).
--It takes 17 teaspoons of pesticides, and I forget how many teaspoons of fertilizers, for a single cotton t-shirt that's not organic. For a set of sheets, it's a staggering amount. Like 1 1/2 gallons (or pounds?) of pesticides. Sorry I can't recall all the stats exactly. I think I have them on my personal site, www.amyfinlay.com
, in the enviromentalism section.
As far as where to find organic clothes, you can search on the greenpages at Coop America's site. Also, I just read that Bono has created a line of "ethically produced," clothing, not sure if this means organic. Probably expensive, but the styles seem great; hip clothes, not just hippie clothes.
Thanks for asking!