You can get them at a arts n craft or hobby store, like Michael's, Hungates, Paul's, it's cheap, I think $2+.

Hey welcome aboard man! Basically it's a technique used on gundam models. You get a brush pen(like a sakura micron brush pen), go over the area like one with panel lines, and generously brush some ink on. Then after a few seconds, or a minute, use a napkin to wipe off the ink. The ink should stay in the lines, and also have a weathered look around the edges. I did this on my Classics Jetfire as well as other Transformers figures and it makes a WORLD of difference. Just make sure to never use a sharpie as I learned the hard way that it will turn purple later on.