Not super familiar with 4 team maps. I know there's
blockfort and
dm_squeek for DM, a few murderball variants out there somewhere, and
flag4sky for CTF.
Just uploaded some murderball maps that weren't on ffpickup.com:
http://www.ffpickup.com/files/ff_murderball_b2.zip
http://www.ffpickup.com/files/ff_murderball_nyro.zip
EDIT: IIRC kingofthetree is also 4-team:
http://ffpickup.com/?p=map&map=ff_kingofthetree