Where can I get LEGO bricks to build a life size wall?
I'd ask someone like Warren Elsmore to help with this. He's done many unique creations for organisations all over the world, and he's written 3 books about LEGO. 

Although I would also consider this idea.
These guys rocked up to BRICK 2014 in London this past weekend and built the walls of their stand with their product of LEGO storage bricks. It worked great. The dimension are huge and still recognisable as LEGO. It would also be heaps cheaper than trying to build it from standard size bricks.