This link might help:
http://www.knmi.nl/samenw/geoss/wmo/...ta_For_NWP.pdf
You can also try looking on the NCEP and ECMWF websites, being the organisations behind the two main global weather forecast models.
I know NCEP use the ACARS data to verify the accuracy of the GFS model output.
It looks like you need to be a member of a non-profit meteorological-based organisation to get hold of the realtime data.