The Red Battalion is a guild consisting of mostly older players, who show up when they have time and interest. The guild hall has both a temple and a stable for the use of anyone in need, and is situated just east of the bridge leading off the Lerilin continent, more or less midway between the Lerilin and Mirith portals.
Immolated is the guild leader, and other notable members include Whisp, Karad, Sheldon, Aderwyn, Shana, Mokey, and Anniqa. There are several others such as Jameson Jinx, Grove, and Yangus, but they haven't been seen for a while. JJ was last seen ghosting around east of the hall, saying oooOOOooo.
The guild is not known to be actively recruiting, but if you are interested in joining your best bet is to play for a couple of years, then seek out and get to know both the leader and some or most of the people listed above, who will then, if they remember, discuss it and perhaps invite you. Recent recruits include Cadfael and Luscinia, two clerics, who try to ascertain there's always enough healing potions to go around, and Nzinga, who is quite secretive about her doings, but often wears plate.