You could try something like a black crayon. That might do something similar.
The only other thing I'd suggest is to apply paint to an item (like a dowel or plastic/acrylic rod), let it dry, then use that to apply rub marks.
My scout holster has all kinds of scuff marks from taking the blaster out.
Also - as a note, and to echo what was said above: make sure your GML knows what you're doing/why you're doing it. You'll get denied at the first glance if they don't know you're going for screen accuracy. Even still, make sure they know exactly what you're trying to achieve.