When using zkl and doing !ring it usually shows what you're downloading (map/mod/engine). You can always download those things directly.
For maps enter
!maplink
in the room chat. Put the mapfiles into spring/maps.
For mods (ZK versions) go to
http://zk.repo.springrts.com/builds/. Put the mods into spring/games
For engines go to
https://springrts.com/dl/buildbot/default/master/. Put the engines into spring/engine.
When you're on Windows you'll find your spring folder at "Documents\My Games\Spring"
Fealthas5: All three of them, engines are mirrored on zk server now and only select ones are available.