Im using S+ industrial grinder and 3 feces gives you 1 sulfur, get a bunch of phiomias and just start a poop farm i guess because I wasnt able to find sulfur aswell.

There is an area with lots of sulfur nodes. From memory, in the south shortly before the Spocalypse biome. It's a valley. The bottom has gas vents and there are high stone arches above it. The nodes are on top of these arches.