I looked into having an aluminum shaft made by a guy who does them all the time. He advised against it since the shaft was so short and the benefit is negligible. Also, he has tried to do them and often they can not be balanced. He said he would try to make one if I really wanted, but no guarantees on it being usable due to the balance issue.
I got my steel shaft here:
http://www.dennysdriveshaft.com/c6_c...iveshafts.html
He knows what he's doing and does a beautiful job.