hmm...haha i actually have never heard of dark adeptus either, but could you simply do some ad mech stuff from the imperial armor books and then incorporate LATD or some chaos contingent attached to it ? :]
hmm, dk have you read a bit on the wikipedia article ? maybe some of the info there can help you get some ideas flowing as well :]
http://en.wikipedia.org/wiki/Adeptus_Mechanicus
-ant