Although this question isn't gender specific, for women you can find them in department stores such as J.C. Penney, Sears, and Macy's. They should also have them for men.
Banana Republic offers high quality cotton pants in both men's and women's styles. This retailer tends to offer clothes in neutral colors, like white, beige, black, and tan. Pants run about $50-$100.
I recommend that you go to Macy's or Dillards they have some really nice clothes and its a guarantee that you will find some. They are both huge stores and have many different sizes. Another store is Palais Royal they have a lot cotton clothing and its somewhere that I shop regulary.
White cotton pants can be purchased from many large stores that have an underwear departments and even from some supermarkets which have not only food but a clothing range. Specialist men's and women's clothes stores often stock them.
