Alex Irvine will be signing copies of Supernatural: John Winchester's Journal during the New York Comic Con at the HarperCollins booth. It might not be an organized event. You will be able to find Irvine at the DK booth on Saturday from 12-1, and at the SF/Fantasy writers roundtable right after that at 1:30.
New York Comic Con will be held February 6-8, 2009 at the Jacob K. Javits Center in Midtown Manhattan, New York, USA.
Source: Alex Irvine Blog.
Supernatural: John Winchester's Journal will be released on February 3, 2009. You can search inside the book by clicking here.