I have a great survival world going right now in Minecraft 1.12 but I can't find any slime. I am doing a project in my world right now that uses sticky pistons. I have searched a ton and I haven't found a single swamp biome. I tried to find slime chunks but I have had no luck. Does anyone have any suggestions?
There are apps and websites with slime chunk finders.
Otherwise you just have to search or dig out a large area underground below level Y40 and hope you find slimes. Once you do you can isolate nearby chunks to see exactly where they are spawning, and that's your slime chunk.
Once you have a slime chunk you can build a very simple automatic farm with an iron golem. You'll need a block of sand, 3 cactus, any other solid block, some hoppers, a chest and some fences. Place the sand wherever you want in the chunk, add the 3 cactus on top, place a solid block on top of that then spawn a golem on top of that and surround it with fences (I find it easier to spawn the golem 1 block higher then break the extra block to drop the golem down between the fences). Surround the area with 1 or 2 rows of hoppers feeding into a chest for collection.
Here is an example I built in my SSP world in 2 diagonally adjacent slime chunks.
When slimes spawn they try to attack the golem and are killed by the cactus, dropping slimeballs onto the hoppers.
You will need to be in an area between 24 and 128 blocks away for the farm to operate, and for best results you'll need to eliminate all spawnable areas nearby so that other hostile mobs cannot spawn (which will severely reduce slime spawns).
The Meaning of Life, the Universe, and Everything.
Here's another possibility that doesn't require much digging. Find a large, underground cavern. You can find a dungeon guaranteed by using an eye of ender. That's nice because then your slime farm can be near an eventual ender farm you might make.
Light up the entire dungeon really well. Turn down your video settings to only render about 4 chunks near you. Wait around and wander. It's best to do it durning the day so that spawns don't happen above ground. You will hopefully see a slime. Figure out where it spawned. If you're not sure, build fences and clear out area a bit.
This let's you cover a large number of chunks without digging out 15x15 spawn beds with walls all next to each other which can take a long time.