I have a Wren industries silent partner for sale. Very good condition, used twice. There's a couple of scratches on it. I've found if I can't find a partner I'd rather go road biking or do something else.
Includes the instruction manual, which is a 30 page booklet to make sure you set things up correctly.
more info here:
http://www.wrenindustries.com/silentpart.html
$125
I'm in seattle. We can meet, or if you're out of town, I can ship if you'll cover shipping.