Any good fabric stores should have them in their bridal dept.If you happen to live in N.Calif ,Beverlys fabrics and crafts have them,in both white and ivory.

Just look in the yellow pages for fabric shops and call and ask if they have a bridal dept,and if they carry the buttons you need.
HTH
Kathi

Here's a link to try. They're not organza covered, but they look nice. Use the search bar to search for covered buttons...I can't make it open to the correct "page".

Here is a link that might be useful: http://www.housefabric.com/categorysearchresultview.asp

The only buttons that I buy to cover are from Atlanta Thread Company

Here is a link that might be useful: Atlanta Thread