Los Angeles, San Diego, San Fransisco, Sacramento CA

Being one of the largest retail economies in the United States, getting used gondola in California shouldn't present much of a problem.

Anywhere near the huge liquidation market, and shipping point, that is Los Angeles CA, you should be able to find a deal on used retail store shelving.

Northern cities, like San Jose, San Fransisco and Sacramento CA, however, are a different matter when it comes to shipping used retail store  fixtures and shelving.  But there are large cities, like Portland or Seattle, which do open a few doors to the north.

The bay area is a huge market, in and of itself, so it will have a fair market to shop for used retail store shelves and other fixtures. 
Spend time checking for going out of business sales from ALL of the nearby cities before you settle for a dealers price, or extend your search out of state
.
Try these nearby states:

Arizona

Oregon

Washington

Utah