for hard-to-stick-to resins and polystyrenes, i make a trip to the local hobby shop and see what primer they have. the item that has worked best for me in those situations, is called mr. resin. i have no idea what is in it, it's all written in japanese except for the mr. resin, but i swear the stuff will stick to vaseline!
you could also try some of the newer krylon products that are made for plastics. even if it's not a primer, it could make for a good basecoat.