Pottery Barn PB Basic Armchair NATURAL TWILL slipcover

I am looking for a reasonably priced new or lightly used slipcover (only) for the Pottery Barn PB Basic Armchair in the NATURAL TWILL color/fabric.

Here is the link for the chair for which I want the
slipcover at the Pottery Barn site:
http://www.potterybarn.com/products/pb-basic-armchair/?pkey=cslipcovered-occasional-chairs

Attached also is a picture of the slipcover I want.
Thanks!