I was just chatting with a scholar who is very fluent in Tibetan about Garab Dorje. Garab Dorje authored two texts in the Tengyur. The first is a Manjushri Namasangiti commentary that is full on Dzogchen without using the word. Apparently it is really interesting.
He also wrote a sadhana called nod jyin gyi gyalpo drup pa'i thab -- which I guess I would translated as the Means of Accomplishment of the Yaksha King. It's in the Tengyur, too.
Vimalamitra apparently also wrote a commentary on the Manjushri Namasangiti-- that is not quite as Dzogchen flavored as the one by Garab Dorje, but in places uses a dzogchen approach replete with standard phrases from the Menagde, but again does not use the word Dzogchen.
Wouldn't it be wonderful to have translations of these texts?
You might be happy to know that the commentary attributed to Garab Dorje has been translated into English by Tulku Sherdor and published as footnotes to Vimalamitra's commentary. The volume, entitled The Wisdom of Manjusri (Blazing Wisdom 2012), also includes Rongzom's commentary as well as a translation of the Namasangiti itself. Here is the listing on Amazon: http://www.amazon.com/The-Wisdom-Manjusri-Vimalamitra/dp/0980173043/