You can always make your own. Coir, Vermiculite and worm castings.
I don't know a place that sells coir t but I don't see why it isn't hard to locate in NYC. But I know you can get vermiculite and worm castings. LES ecology center sells worm castings and Home Depot definitely has Vermiculite. Either 57th street location or 23rd. Bigger stores out in Queens and BK have bigger gardening dept. Its your run of the mill miracle grow brands though.
Or just use potting mix. Organic Mechanic Bag for $5 at Whole Foods in Union Square. Its vermiculite, compost, worm castings and coir.