"Niko's Fuel" quest uncompletable [SOLVED - somehow]

Title.

Niko's Fuel quest tasks me with collecting (0/5) Voltaxic Sulfite. However, it doesn't spawn in the mines. Fine, I visit the mine encampment and have 100 sulphite somehow, which allows me to complete the subsequent quests (craft dynamite/flares, blow up a wall, upgrade darknessres/lightradius). However, the quest in act 4 still shows up to collect the sulphite.

The problem comes when I have played from act 4-act 10 and Niko HAS YET TO SPAWN AT ALL. I'm afraid I won't be able to collect sulphite at all! Has this bricked my game?

Thanks.

-UPDATE-
Niko showed up in the second to last zone of act 10. I'm not sure why he didn't show up for 6 acts before that. *shrug*