I obtained all 50 as transport passenger mission rewards in Aditi whilst working on my Empire rank. They were always to the neighbouring system.
CNB ?
I got my 50t in a single session with a mining Orca in the high RES around Delkar 10. OP is very unlucky.
Saturn has it too I seem to remember...
No kidding ran out of limpets at 49.6 tonnes the other day. Then found out about permit. Pro tip don't go farming rep in a compromised nv beacon in an anaconda full of bromilite that spawns a tonne of elite cobras
Is there no bounty hunting res site with the faction that grants the Alioth permit or are you forced to do boring missions only for them?
edit - just saw a mission to deliver 88 bromellite. Take a mission like that and abandon. I think the engineers accept pirated goods as donation.
First up, do you have the Alioth permit? Don't waste time mining if not.
20 prospectors used isn't that many, just keep looking, you have been a bit unlucky so far
Good luck!