How do you get master chiefs armor in halo reach?

Answer 1

Play continuously enough to gain the ranks require to unlock the armor he wears. I believe you should have all his armor by brigadier or general [give or take a rank or two] once it is visible AND unlocked you need the amount of credits required to get that helmet to wear.

Answer 2

There are only a few armor pieces available that were worn by Master Chief. This includes the MJOLNIR Mk. V shoulder pieces, which require a Brigadier ranking, 100,00 credit for the left shoulder piece, and 80,000 credit for the right shoulder piece. The remaining armor is the MJOLNIR Mk. VI helmet piece, which requires a ranking of Brigadier and 300,000 credit.