can  you get a seat like this somewhere or did he make it....if he made it what is it made out of.  
http://tuxserver.dyndns.org/%7Emartin/gs500e/index.html

Well you can get something very similar by adapting the tail from an R1 or R6, something along those lines. JamesG makes a tail section similar to that also. Another choice is to get a solo tail that just covers the rear seat with a fiberglass piece that gives the illusion of a solo seat. Check Pantablo's site and the wall of fame for examples.