While they are known of, it was not possible to successfully separate them from the trees which they grew/lived on without knowledge of certain methods for doing so. These methods were only developed in the period after the fall of the Galactic Empire, sometime during the Thrawn Campaigns, or a little earlier.
While this is true, and I don't know the details, wouldn't it be possible for G0-T0 to find this solution as well? If he actually took a vested interest in the lizards, couldn't he develop a way to get them off? Is what Thrawn did super-special, and unable to be replicated by anyone else?
In fact, Thrawn was not the first one to do it, a group of smugglers found the way to remove it. So it stands to reason that G0-T0 could still aquire these things, seeing as he's (probably) more skilled and knowlegable than the smugglers that figured it out. Maybe send his Zhug Brothers to gather them?