Found an A2 upper that is a grey color and has the letters CMB on it. What make is this??

This link might help: www.biggerhammer.net/

Go to the AR15/M16 FAQs

I didn't check the Bigger Hammer website before starting this, so you may have already gotten all the info you needed. If not, I can tell you that it's a Colt early A2 series upper (C=Colt)
The MB indicates the forging people Colt used on this piece. My own Colt A2 upper is only marked C M. (Gee, maybe yours is better than mine. You've got an extra letter ) I say early because of your description of the color. Anyway it's a good unit. Hope you get much use from it.