REI sells backcountry gear for sure. They have stores in Jersey. I think winter stuff is going out at their locations.
Otherwise, if you are looking for backcountry specific gear, like packs, beacons, poles,probes, shovels, find a local mountaineering shop. Pretty much your best bet for that type of gear. Hence the REI recommendation.
I also forgot about EMS, since they closed all their shops around here. They are still a big presence on the east coast. Similar to REI, just not as big of an organization. Looks like they have locations in NYC and beyond.
Thanks KC. REI is opening a store in SOHO in November which would have been sweet. Don't think I will get off the island as I am only there a couple of days. EMS has a store on Broadway though so I will check that one out for sure.