I have seen them show up on evil bay from time to time. They seem to go for quite a bit of money, like around $2500 for the whole setup. I don't know of any for sale right now. I can suggest three places to check, although it may be a waste of time.
1. The only actual Alfa 6 I have ever seen was down at Shade Tree
http://home.earthlink.net/~fiatdr/shadetree.html . However I don't think it was a parts car. It was actually a bullet proof Alfa 6 (armored everywhere but it looked stock). I guess I would try there first.
2. I would try contacting one of the South Africans at
www.alfagtv6.com .
3. Danny at fun imported
http://www.funimported.com/ seems to be able to get anything. I don't know how he does it, but my dad has ordered some really strange stuff and this guy always comes through. Sometimes it takes a while, but he seems to have some contacts in Italy nobody else has.
Good Luck!
Greg