Wimberley makes one, too:
http://tripodhead.com/products/p5-m8.cfm Maybe Kirk and/or RRS do, as well.
This is only needed if wanting to attach the camera body itself to the gimbal head, when using a shorter lens that doesn't have a tripod mounting ring (see illustrations at the above link).
And, you must first have an Arca-Swiss style camera plate on the camera body (there are generic plates, as well as those custom made to fit particular camera models. For example:
http://www.kirkphoto.com/Quick-Release-Camera-Plates.html).
And, the above Wimberley accessory will only provide horizontal/landscape orientation, unless an L-bracket (such as this:
http://www.kirkphoto.com/L-Brackets.html) is used on the camera.
The above aren't needed if only wanting to use the gimbal and tripod with a long lens that has a tripod mounting ring.
However, unless one is provided with the gimbal head, a lens plate will be needed... It typically needs to be a little longer than the "foot" of the tripod ring on the lens, so that the lens/camera combo can be slid forward and backward slightly to achieve equilibrium. For example, this lens plate is designed for use with a gimbal head and the Sigma 120-400 DG OS HSM lens in particular:
http://www.kirkphoto.com/Lens_Plate_for_Sigma_120-400mm_f4.5-5.6_DGOS_HSM.htmlThe "problem" with a full gimbal mount is that it makes a tripod relatively "large lens dedicated". I.e., another approach to allow use with short lenses would be to change out the head for a standard ballhead or pan-tilt head. That's not always convenient or practical.
Some gimbal heads mount to the side instead, which does allow vertical mounting of a camera and short lens (but doesn't allow horizontal/landscape orientation of that combo). Examples: Kirk King Cobra (
http://www.kirkphoto.com/King-Cobra.html) and Wimberley Sidekick (
http://tripodhead.com/products/sidekick-main.cfm).
The Sidekick actually just fits into an existing ballhead, instead of replacing it completely. This makes switching back and forth between gimbal usage with long lenses or ballhead-only use with shorter ones very simple and easy. The Sidekick is a bit limited on the size/weight lens that's recommended to use with it... And it really needs to be used with a fairly sturdy ballhead.