TBRC is going to be your best friend in cases where you specifically want the Tibetan of certain texts. I highly recommend you get an account there if you don't already have one. Not sure how much of Guru Chöwang's works have been translated into English, if any.
This is the entry for the "Collected terma revelations of Guru Choewang": http://www.tbrc.org/#!rid=W1PD45090
And there are 99 results for texts regarding Khorwa Dongdruk: http://www.tbrc.org/#library_BannerSear ... rugs"
However, searching for both terms yields 0 results, so it's possible that the "Collected terma" is somewhat incomplete, and the only terma on that deity in their database is the one from the Chokling Tersar... Does anyone have better luck than I did in finding it (perhaps someone whose grasp of Tibetan goes beyond the syllabic)?
In any case, happy hunting!
"The Sutras, Tantras, and Philosophical Scriptures are great in number. However life is short, and intelligence is limited, so it's hard to cover them completely. You may know a lot, but if you don't put it into practice, it's like dying of thirst on the shore of a great lake. Likewise, it happens that a common corpse is found in the bed of a great scholar." ~ Karma Chagme དྲིན་ཆེན་རྗེ་བཙུན་བླ་མ་རཱ་ག་ཨ་སྱ་མཁྱེན་ནོ།