You might try shopgoodwill.com - more vintage stuff than you would typically find in the average Goodwill store, and Etsy has a surprisingly good vintage section. It really depends on what you're looking for.
You may just have to spend a while on google browsing around for what you are looking for. There are a large number of shopping sites dedicated to vintage stuff, you'll just have to really look. Some neat stuff is out there!!
Decades has a blog which lists their latest designer vintage items for sale; you can communicate with them and buy these pieces via email or over the phone. They have some very beautiful and rare items: http://www.decadesinc.blogspot.com/