All of the above is excellent advice on custom controls in LabVIEW. National Instruments also has an Application Note located here,
LabVIEW Custom Controls, Indicators, and Type Definitions. Check this out for more information about creating your own custom controls.
In terms of finding custom controls already created, do a Google search. You should be able to find quite a few websites that have custom controls for free. It's just a matter of finding the one that fits your needs.