A real servo-based cruise is indeed available from mccruise dot com.
(10% GST will be added in the cart for Australian orders only) The Motorcycle Cruise Control unit is specifically designed for this vehicle. NOTE: - This product will fit Roadster models (with footrests instead of foot-boards) with some modification to the mounting of the cruise control throttle...
Any halfway decent mechanic should be able to install that. I've been thinking for years about doing it myself but haven't been able to tour much anyway these past couple of years because reasons.
A real cruise is always vastly preferable to a throttle clamp. The instant you touch a brake with a real cruise, it disengages, even if it's the rear brake. It also adjust for hills and you can tweak the speed up and down with more precision. I'm not personally a fan of clamps, I just use a throttle boss. Similar effect but at least if you release the throttle grip, the throttle goes to zero.