So many airlines are retiring planes. Call them up and ask. There are also airplane junk salvage yards were you could pick one up. Go to Barnstomers.com and the have a section for the sales of commercail jets and E-mail some one who is selling parts they will find a seat for a fee.
I don't think you will get away with taking one of the plane. I only take headsets and blankets and pillows. I do not steal them but request really nice and as no one normally ask and just takes them they normally thank you and say have it for free.