Knight,
It's a very NOT fun and tricky business to remove the bezel from a SureFire light. And cleaning from the reflector bore is also tricky and prone to going wrong in a hurry. Some compressed "air" products can actually leave a film on the surface of the lens and reflector. I've had this happen to me. If you want to go this route, make sure that your can doesn't warn not to use on optical equipment.
But listen, how big a deal is this? A few dust and debris particles? FWIW, my suggestion is that if it doesn't affect beam quality or steal any light, JUST LIVE WITH IT. Get over your insanity. Your M6 head will function just as well with a bit of dust in it, as without.
If you just can't get over it, and it's driving you insane, then you'd best send it back to SureFire, because chances are good--more than good--that anything you do to remedy the situation will only make it worse in the end.
Bottom line: live with it as is, or send it back. Those are my suggestions. And I'm not afraid to modify lights or take things apart, by the way. I'm just realistic about how difficult it is to achieve the kind of perfection most of us here at CPF are looking for. Even just cleaning--REALLY cleaning--a glass lens to perfection can be difficult. And cleaning reflectors is even more of a nightmare.
Just be careful. Remember the first rule: DO NO HARM. Don't make the patient worse.