Ive searched for these too, and have good news for you... THEY ARE THERE, well at least the Dead Orbit ones are being found. Bittersteel and Revnant have both been attained through LVLing up the rep. Its still slightly random but seems there is a range. Ive seen 4 verifications of recieving Bittersteel from rank 6, 8*2, and highest was 11. Revenant was higher up at rank 14 reward I believe. That would suggest to me that the otherfactions are probably keeping theirs at higher rep levels too as rewards, but I havent seen anyone who cares about the other 2 of any rank yet.