there not that rare i have only seen maby 4 people in my time on skyblock not have a chunk i restarted i have 5 already and my island befor that had 5 you just have to find them
They can be rare. Normally people have 1-3 slime chunks, but twisted got 5 Q_Q and usually about 1/100 people get 0 or 1/2 of a slime chunk. Best way to find them is to build a 99x99 platform at y = 1-30
Twisted is right, they are not as rare as some people think. I have three slime farms over four different chunks and pretty much my entire lower level spawns slimes. It's kinda crazy actually. But yeah, you should definitely have a few at the very least.
To expand on the finding them part build a 99x99 platform on floor 1 then mark out all 16x16 chunks with fences or 2 high walls and if a slime spawns in a 16x16 chunk you have marked then that is a slime chunk where you build your farm if you need help let me know in game or I can link you some vids on the building of the actual farm
