there is no special scanner for materials in supercriuse. Just hop in a signal source, pop up your, left handed, contacts-tab and see whats out there. If its fine, lower your cargoscoop and scoop the materials with a speed <40m/s. If your lazy, get some collector limpets doing the hard work (scooping) for you. Simple as that.
Edit:
Another tip. If your looking out for something special, get to "Inara", search the material you want to obtain and the site will give you tips in wich USS you have the highest chance to get, what your looking for.