Can paint/hardware stores match stain like they do paint?
I would buy something close and tint it yourself.  You can run sample swatches on scraps of your unfinished lumber and stop when you get it right.  This will also allow you to experiment with different techniques to see which is the best match, e.g. how long to let the stain soak in before wiping it off.

See http://www.ehow.com/way_5938323_can-add-tint-wood-stain_.html