the link wouldn't work for me so I'm working blind.
got some silver paint from a 3dmg prop on it at a convention
Unfortunately, this sounds like the prop wasn't sealed correctly, which is why stuff rubbed off of it. The good news it this likely means the stuff on your jacket isn't down deep into the fibers like wet paint.
Take the jacket to the kitchen. Use liquid dish soap (the kind you use by hand, Dawn or Palmolive, or whatever) put a dollop of the soap straight on the stain, gently rub it in with your finger. Set a timer for five minutes, go do something else until the timer beeps. Come back and use a gentle brush (old tooth brush, a nail brush something like that) on the stain then run it under cold water, continuing to scrub.
If this is partially successful but didn't get it all, just repeat until you get it all.
Rinse thoroughly, hang to dry.
Oh, and go seal that prop!