The little buggers do not want to come out though, it's half term next week so going to see what I have at work to persuade them to come out (as I want the rings and cage still)
Though you may be able to buy some as they look like a normal screw-bolt that should be available.
My understanding is that first gen M900 cassettes held together with lots of small screws often sheered - hence the sudden demand! Second gen are riveted. I'm trying to salvage a Ti cassette that some kind soul sold me without mentioning the fact that four screws had already snapped on the third cog - good karma to you buddy....