I second SurferGeek's needle file suggestion.
I have a set of diamond needle files that I have used on plastic, metal, wood and resin. The metal files I had before were a little too rough on plastic and resin, but the diamond files work great. I picked my set up at a Cummins Tool sale for $10.
In case you're not familiar with Cummins, they are a traveling tool show that sells closeout or cheap but useable (sometimes) tools. Great place to pick up items/tools that you may only need for a few uses.