I don't mean any offense by this, but based off this thread I would strongly advice that you take some time to read about this method before taking action. Jumping in to any method without knowing what you're doing makes it likely that you'll survive and instead acquire a new set of problems.
You probably won't be able to get nitrite by tomorrow. It's not a pharmaceutical, and the only physical stores that sell it are butcher shops or any place that would offer supplies for meat curing.