There are *many many* places to buy beads online:
http://www.google.com/search?q=beads+shop+buy
And btw, I diagree with a previous answerer...you *can* use buttons or any beads or any other thing you've purchased to sell again, whether they're fancy or not (alone, or as part of new jewelry you've assembled, or another work, etc).
Once you've bought something, it's yours...however, you just couldn't (legally) use that bead to make a mold for more of the same, or claim you made it, etc.
You can also make your own beads from *all kinds* of different materials.
For example, polymer clayers make beads of all kinds/shapes/colors/etc, which can even look like other materials--e.g., metal, wood, jade, pearl, as well as just making any color, pattern and shape:
http://images.google.com/images?q=polymer+clay+beads
http://glassattic.com/polymer/beads.htm
http://glassattic.com/polymer/pendants_cording.htm
(and you can even make buttons from polymer clay: http://glassattic.com/polymer/buttons.htm )
For jewelry "findings" though like ring blanks, earring findings, chains, etc:
...check out online suppliers listed in the link called "Supply Sources" near the bottom of this page:
http://glassattic.com/polymer/jewelry.htm
(Some findings will be cheap and some expensive if made from certain metals, some places will require buying in bulk or a wholesale license, some will be huge and some smaller, etc.)
...or you can find many findings at craft stores like Michaels, etc., or in "bead shops."
...or many people make their own findings from wire, which is lots of fun as well:
http://glassattic.com/polymer/wire.htm (click on *Basic Wire Shapes*)
HTH,
Diane B.