A tga file?
As it's a file graphic format for image, you must redraw your object in a 3D prog and then save it as "image" in file format image (psd, tiff, bump...)
As the tga file is generally absent you must reload your psd, tiff, bump in a 2D prog for save it as tga :)

or make a screenshoot in the moi export obj shaded mode or not (or at any moment)
you save the screen by pressing the key "Print Screen" of your computer
so you can put it as a of the Copy the clipboard in your favorit 2D prog :)