Fight your way out; only scrubs and mashers jump out of the corner
In all likelihood there is no more spare artwork from Halo hanging around Bungie that isn't on display or something. There was pretty stiff competition with Bungie employees for some artwork on auction at A Night with Bungie, which should be an indication: if there had been a lot left, senior Bungie employees wouldn't have had to buy it at an auction Bungie was hosting.
Any spare artwork laying around is bound to be from Destiny, which Bungie wouldn't want to spread around outside the company yet.