Try Ebay, I buy 5 kilo bags of washed white rags, they're old hotel and hospital sheets cut up. A bag lasts me at least two years as a full time furniture maker.
we got a bag of old clothes that are supposed to be just that- lint free rags..
when something gets old, or no1 wants to wear it again, we don't bring it to donation stores where they ship them abroad and give the charity 5% of their earnings and claim that they are doing such a good job, instead I Use the old clothes as rags..