80/20 has an "AutoQuoter" program that is supposed to have all of their extruded aluminum products in it for designing. The only problem is that they say it needs AutoCAD, so I'm not sure if it will work with Inventor.
"Understanding AutoQuoter:"
http://www.8020.net/peace/autoquoter.asp
"Using AutoQuoter:"
http://www.8020.net/peace/usingaq.asp
Good Luck!