It can be farmed right now. Zato just said he has found 12 fccs and Bantz described how he had put some serious time on finding them. Farming equals repeating the same tasks dedicated for one thing only over and over again without much of a risk. I basically farmed my fcc by entering a map, checking for a car wreck and getting out. If fcc was in a "dungeon" type of map as I described (an ancient highway) it wouldnt be riskless anymore and one wouldn't simply browse through the place due to the fact that there were others after the exact same item + possible npcs. If the chance finding fcc from that highway place was equal to current, the total ammount of fccs wouldn't suddenly soar.
actually, i have never farmed FCC's specifically. like i said, and as many unfortunate newbies are aware, i spend most of my time in the boneyard. through the course of leveling up and farming, i have encountered that many car wrecks with FCCs in them. 12 is just low balling it, i stopped keeping track after a while. my point is, they are not as rare as you would think, and you will pass time much faster if you do not attempt to 'farm' FCCs, but rather, play the game and let the wrecks come to you.
now, i run ambushes all throughout the boneyard, and in searching for an ideal map or encounter, i am usually able to find FCC's sparingly this way.