This plugin was probably for Gamespace. But Gamespace, older trueSpace versions and most of the plugins is not longer available since tS7.6 went freeware.

A working art pipeline is via OBJ format. Here Blender and the MDL7 export can come in handy. Because OBJ arrives in MED without textures. Blender reads with textures though. But this solution is just useful for static stuff. Or you own Ultimate Unwrap 3D, export from tS 7.6 as Collada, load it in UU3D, export as FBX, load it in MED and save it finally as MDL.

There is also an FBX plugin for trueSpace in development. Means when this arrives UU3D is not longer necessary for conversion. But this development can last a while. The guy who writes that plugin is currently busy with something else ...