There's a bit to break down here, others have helped you with the FSS and finding the DSS for sale. I'll look at this bit:
OK - assuming you're in the Bubble, you won't need any of your scanners to scan for minerals.
Open your System Map, and open the DATA tab shown with the red arrow here:
View attachment 180635
This shows you valuable information of the makeup of a body.
Click each landable body in turn (the ones with cyan arcs around them) and scroll to the BOTTOM of the information on the left. Look for - in your case - sulphur. The higher the value assigned, the more likely it is you will find what you need.
Fly to that body, land on it, deploy your SRV and have at 'er, baby!
No FSS or DSS needed.
When combined with EDDB or Inara, you can find the mats you need quickly, easily and enjoyably, if you love running around on the surface - and I do.
Cheers!