Here you can book a half or full day bus tour that includes a visit to the famous Keukenhof, and to the flowering tulip fields near Amsterdam.
Only available during April and May, when the Keukenhof is open.

Web:
http://www.partner.viator.com/en/2064/tours/Amsterdam/Keukenhof-Gardens-and-Tulip-Fields-Tour-from-Amsterdam/d525-2550LIN12A