This one is up-to-date, but it doesn't have future constellations:

http://hacks.atrus.org/neopets/findConstellations.fcgi

However it has been seen that most of the constellations will have at least one big/bright star in it (as opposed to the normal white stars), so if you use the Ye Olde Star Mapper site and put in your star data and then uncheck the white star option, hopefully you'll be able to see the locations of the constellations you haven't found yet. (As at least one of the stars in every constellation seems to be different)