I had the same problem and ended up using my impact wrench to get them out... It tore the sproket when it came out. I've only seen aftermarket ones, Renthal etc, without them, so not sure. I had a new Honda one to stick on though, although I was aiming to use an alloy Renthal at the time. Be interesting to find out what you're supposed to do with them!
_________________
NSR300R - Why did i ever have a 250...