I have a linear damper like that on my Ducati Monster after getting spooked by some head shake.Hyperpro makes one, and the mounting kit to go along with it.
Mounts on the left fork leg and the frame on the left side.
Here is the mounting kit:
The link to the damper is also on that page.
As far as price goes, let put it like this: They are very proud of it.
...sometimes on the motorway but I have never experienced a tank slapper.