Providence, Warwick, Woonsocket

You usually want to scan craigslist (website) and other classifieds for store fixture liquidations.  Check first in Rhode Island, then scan Massachusetts and Connecticut.

You next closest used fixture dealers in Boston.  Right around the New Jersey area you will find dealers starting to pop up on the map (NY, NJ, PA, MD...), but the shipping costs start to rise in the traffic jam.
Try these nearby states:

Massachusetts

Maine (yes)

New Jersey

Pennsylvania