Don't know of any libraries of buttons, sorry. You can always do your own. I'ts not particularly hard. Anything you see or can imagine should be doable.
Mike...
Certified Professional Instructor Certified LabVIEW Architect LabVIEW Champion
There is only one page that I know of for downloading Custom Controls: Lab-Useful - Custom LabVIEW Controls. It isn't anything to write home about, but it has a few nifty controls.