I assume (from the look of mission tables & whatnot), that the game rolls on a table of rare mission once every 7 days (ie, 7 day cooldown after turning in the previous mission), and Blingtron & Champion's Honor token amongst other are on that table, hence why you never see more than 1 such rare at a time, or why there can be a long time between specific missions (because rngesus).
I had Blingtron mission pop up 4 times this week, 3 of them on same day, which would fit my early batch of chars all having rare long cd missions popping up at same time in the past.