Well...it's kind of hard to say without first seeing the coins.
Brass brush (soft) would probably do the trick, unless it is really crusted up then you will just end up polishing the high points. You could attempt electrolisys, but i have never
had a lot of luck with it and especially not with coins I want to actually
flip.
I guess the long and the short of it is there are many chemicals and processes you could use, but you run a great risk of ruining the coin when patience will really pay off in the end.
Post a pic or scan if you can and you will (I'm sure) get more satisfactory responces than mine.
Chris