I just avoid setting the goal of doing it so early into the patch. Save myself the trouble and focus on other aspects of the newly introduced content, some of which does involve hunting non-mark elites from time to time. I guarantee that within the next month or so, it'll become a lot easier to hunt down the targeted mark. Part of the reason being that I don't think a lot of people realize that every zone has a B/A/S rank elite in them, and the reward for just killing them greatly outweighs the reward for the mark.