Microchip Direct (
www.microchipdirect.com) is the only place our team has been able to find them. They do typically ship from Thailand, so timing may be an issue if you want them for NYC. Also, I don't believe the surface mount packages (that's what the "-I/SO" means) are in stock.
We are using a DIP package as our backup. It's pin for pin identical, but lead spacing and other things are different, so some wiring has to be done.