Most of carpet stores install a new carpet and take old carpet for recycle. Those old carpets still in good condition.
Every carpet store has a big container to recycle old carpets, remnant, sample of carpet.
I have a big back yard 5000 square feet. Therefore I often need a large amount of carpet to cover all backyard. I go to a near carpet store and ask whoever is working there about old carpets. They are glad to allow me to take carpets, because anyway those carpet go to recycle.
So if you need carpet, remnants, you just only find a local carpet store and you will got any size carpet to fit your condition.
Hope this small article help you.
For other purpose we can help to reuse old carpets from landfill.