Done Magma slime islands?

I have spent a good amount of time searching for the magma slime islands in the nether and haven't found one yet. Other players haven't found one either. I have created singleplayer worlds and searched for them there. Found many in every single world. Are we just unlucky that we haven't found any or are they disabled?

 

What is on those islands that is useful? I'm curious

 

So what am i supposed to do? how do i get magma slime?

 

99% sure they spawn in nether fortresses.

 

I don't mean magma slime as a mob, but there is a kind of slime ball called "magma slime ball" or something. You get them on the magma slime islands as blocks.

 

they have slime blocks and can be used to make tools and stuff. its pretty great

 

Could it be possible to reset the nether so that the magma slime islands do spawn? Or maybe set up a shop where i could buy congealed magma slime blocks? If that isn't possible then somehow trade with admins?