They are rare because the size of the patch of atmosphere that can be corrected by a given guide star is so much smaller at shorter wavelengths and changes faster - so you are either limited to where you can observe (near a bright guide star), or you need complex and expensive laser guide star systems.
If you are purely imaging (rather than trying to use AO to feed a spectrograph) there is a common alternative. You image the object continually but only use those images where the atmosphere happened to be still enough to briefly give a good image. You can do this either by reading out the CCD in short exposures or using a separate shutter.
You can combine this with a simpler AO system to make a "good" atmosphere into an "very good" one - eg the Magellan telescope has a visible AO system
The other big driver against a visible AO system purely for imaging is that you can always use the Space telescope instead.