Definitely have a look at eBay.

Just be careful that you get accurate measurements from the seller cos a lot of the new clothes are seconds which have come up large or small on manufacture. For instance I recently bought three pairs of brand new with tags Evans jeans. The seller said they were labelled as a 22 but when they arrived they were more of a 24 (which was okay at the time).
Some of the more business-like sellers offer a refund/exchange if you buy something which is too big/small for you and, of course, you can always sell on your clothes when they don't fit any more.