I desperately need slimeballs. Most of my farms can't work without it. If you manage to find a really compact slime farm, (i.e one that doesn't take up a whole chunk because mining all of it would take a long time) please let me know.
Also, I'm doing this at night, no light sources, and I have never found any slimes in my world. I am also searching for layers 70-50, which I believe they spawn there in swamps.
Keep in mind that slime spawning in swamps depends on the current moon phase. Look at lighting up nearby biomes and adding surface area in the swamp to increase your chance of spawns. In my personal experience swamps are the best way to get slimeballs.
...However come to think of it I have not seen any slimes in the swamp I'm located in since we switched to one of the newer patches. Wondering if there's a bug there.
The Meaning of Life, the Universe, and Everything.
Slimes should spawn when it's a full moon
"In swamps, slimes may spawn at night between the heights of 50 and 70 provided the light level is 7 or less. They spawn most often on a full moon, and never on a new moon. Slimes spawn in the normal swamp, and not in its variant, swamp hills." ---Official Minecraft Wiki