If you want to find servers online, here's my advice:
and download their free software.
Then visit the JK and MotS rooms and look for people to play with. May take some patience but believe it or not there are people who still play there (and I like their software better than the Zone, which no longer supports those games anyway).
Additionally, you can download Qtracker and use it to add IP's of people you know who host servers.
The thing is, JK/MotS has no dedicated server support, so it's asking a little more of somebody to host a game 24/7 (since they have to be in the game with you).
So find people, buddy up and talk to them, relive the nostalgia, and that will get you into some games sooner or later!
But, it's fun, and you should take the time to play a full game at least a couple of times. ; )
Otherwise try setting up a small "LAN Party" with it for fun. It's a fast fast game, and has low system reqs, so anybody should be able to play it. Plus it's better on a LAN anyway in terms of ping.