Slimes only spawn in certain random chunks & below layer 16. To find which chunks in your seed have slimes use this tool. http://extension.ws/...aft/slimes.html The tool tells you the X,Z coordinates for the corners of each chunk, so you just need a map. The best way I was able to farm them was to find 2-3 chunks near each other and then start at level 16 and make several more "floors" going down, each 3 tall. and totally encompassing the "slime chunks."
