Don't know how thin you need them to be, but Lee Valley Tools has some. I've ordered from them a few times and their service is excellent.
Here's a link to the ones which might fit your project: http://www.leevalley.com/wood/page.aspx?c=2&p=32065&cat=1,42363,42348&ap=1' rel="external nofollow">
Rare-Earth Circular Magnets
The company is in Canada but they ship to the US.
Hope that helps!