Okay. There are two brake lines in the front. One for left one for right. In the rear, only one leaves the master cylinder, which then runs to a splitter. From the splitter, one goes to passenger side, one goes to driver side. If you were to buy a "passenger side" rear brake line..well, I didn't know they sold just that. But that would be, in my best guess, the short one that goes from the splitter to the brake drum. If the main one going to the back needs replacement, thats a big long one. I did my brake lines, except for the two short ones in the back..I just bought two 25Ft coils of brake line, a craftsman double-flaring tool, and the second coil of brake line came with all necessary nuts. It wasn't bad at all to learn how to flare it right on my own at all. Used the old brake lines first to get practice (and broke a cheap flaring tool in the process...get a quality one, spend the extra money. It's worth it) and just went from there. I also replaced the front brake hoses. I know, that was alot of verbiage...but I hope it answered your question sufficiently, and gave you more information that could be helpful. If it didn't answer it, provide more information and I'm sure myself and others will be more than willing to help.
Also, the reason I went with making my own is that to get the brake lines already made, I would have had to buy the pre-bent entire set for MUCH more than I spent doing it myself, even including the cheap flaring tool that I broke, and the craftsman that I bought after that. If you go this route...might as well replace them all, not just the one that needs it, just to be safe. The rear brake lines are short, and pretty direct- You shouldn't need to bend them at all. For the others...use a pipe or a socket and bend the lines around them, so as not to kink the lines. Also, if possible, buy stainless steel brake lines. I believe the pre-bent, plug and play ones are usually stainless. Also, they don't require you to flare and put the nuts on yourself.
If it helps much, I'm 17. If I can figure it out...I'm sure you can.
A good, reputable (well, in my opinion. Never had trouble with them) dealer in this sort of thing is Quadratec.com. Others are 4wd.com, jcwhitney.com, and I'm sure there are others out there that I'm not familiar with, but others are.
Good luck, and (I'm assuming you haven't had it for long) welcome to the world of jeeps.