There's nothing particularly illegal, immoral, or crazy about buying a used CD. However, I'm not sure asking on a notice board is the easiest way to go about this.
Is there a reason why you ask here? Obviously, you have internet access, which means you also have access to sites like Amazon or Ebay, though you may not have the means to purchase these items online. In that case, try used CD shops or old record stores.
DJ's the man we love the most