Although completely cheesy...I've found a lot of neat buttons at Wal-Mart and Hancocks in the La Mode Vintage line. They have various designs and styles that are supposedly from a certain year or decade. They do have a really nice weight to them. I found an online shop that has them: http://www.shopatron.com/index/511.0.215126.96.36.199.0
Also, here is a site that I always find helpful for anything: http://www.costumersguide.com/costume_research.shtml
I've noticed that a few times when they couldn't find exact buttons, they would take the plastic black ones you find at Wal-mart and use a paint pen to change their look. Probably not the most pertinent information at the moment but it might come in handy.