These plates are around $250 each, and are sold to normal civilians rather than being restricted to law enforcement or military.
http://www.youtube.com/watch?v=cKprcAno1bo
Regarding maintenance, the rules of thumb that I was told by the sales guy, and which are repeated in the documentation that comes with the plates, are these:
1. Try not to get the plates wet. If you do, get them dry again in a hurry.
2. Try not to train too hard with those particular plates, as all armor plates are somewhat delicate. If you want to emulate the weight for crash dives or whatever, they sell training plates, or steel plates, or I guess you could just shove some weights in the PC. Anyway, you can train with the plates you rely on, just understand that they're a little like a fire extinguisher, they're best when they're previously unused.
3. A simple test of their condition is to tap a quarter against them in a number of spots. The tap should sound about the same at each spot, and feel solid. As in the video above, if the plate starts coming apart, it's going to spread out and soften, resulting in a more muffled tap.
They are not the only plates BPF sells, nor is BPF the only source for plates. But those are the ones I trust.
(If you do get those, remember that some plate carriers, like the Eagle, are cut so that you have to use two front plates, rather than a front and back plate.)