Where to buy hickory and other wood on Long Island

Have you tried craigslist?
http://longisland.craigslist.org/search/?areaID=250&subAreaID=&query=firewood&catAbb=sss

Also check out the free section on craigslist. More times than not after a storm people will post "You cut it. You can have it"

stop by an apple or peach orchard, they all have scraps, and most are willing to let you take it away. Also, if you're in a pinch check out http://www.lifirewood.com/long-island-firewood.php more pricey than scavenging for your own, but they have a good selection. I use their kiln dried wood for pizza ovens on the weekends at jamesport vineyards