My vote so far would be either for "rabble" (as it is something that has been used already for some time on this forum), or "sett."

I like "sett" because it alludes to common tartan terminology, yet at the same time sounds like a group of something. "A sett of X Markers."

Those suggesting names like "X-patriates" and "X-philes" miss the point (though those monikers are clever). The point is to come up with a name for a group of X Markers gathered together, not a name for X Markers themselves, singular or plural.

Think in these terms:
-Pride of Lions
-Gaggle of Geese
-School of Fish
-Herd of Sheep
-Murder of Crows
-Flock of Chickens
-_____ of X Markers

So far I vote for either "Rabble of X Markers" or "Sett of X Markers."