Utz Crab Chips?
This isn't south of Union Square, but I can recommend trying Westside Market in Chelsea because it's one of the few places I know that carries a large selection of sometimes difficult-to-find chips.
Link ---> http://www.wmarketnyc.com/contactus.html
As a substitute ... Zapps (from New Orleans) CAJUN CRAWTATOR
Zapps flavors ---> http://www.zappsstore.com/cgi-local/S...