Bordertown Displays (website) (new grocery store fixtures, not gondola style but maybe helpful)
There aren't any used gondola shelving dealers in North Dakota. Don't act so shocked.
Try craigslist (website) to look for store closings in Fargo, Bismark, Grand Forks and Minot. Your next step, should N.D. fail you, is Minnesota. Review any sales, and get prices from dealers.