Jason, I am in the process of replacing the brake lines in my truck right now. I had to disconnect the rear lines for a differential swap, and had to replace the front lines to install Charlie's disc brake kit. I had all the original brake lines in my truck, and most of the rusty lines snapped when I disconnected them. I decided it was time to replace all of the brake lines.
The brake lines are 1/4" mild steel tubing which is available in various lengths with the correct fittings at any auto parts store. 3/16" will also work for you. It's also available by the roll. If you want to replicate the original lines, you will have to cut the tubing to length, bend it to shape, and make a double flare at the end. Decent flaring tools start at about $30, tubing benders are in approximately the same price range. With a little practice you can bend your own lines and make flared ends that will not leak.
If you don't want to bend and flare your own lines, there are vendors like Classic Tube or Inline Tube who will provide pre-bent and flared lines. You can send them your old lines and they will replicate them for you. Expensive- several hundred dollars, at least. You could also have a local brake shop do it, of course.
Let us know how it goes!