Have a look at the IARU Region 2 Band Plan. Most of the frequencies marked "all modes" or "DM" (digital mode) may be used for packet radio, although there does not seem to be a single designated packet calling frequency.
Normally a packet radio frequency is coordinated between operators in the area, since one frequency can be shared by several TNCs. In this case the frequency is standardized ad hoc and won't necessarily be the same everywhere.
You should be able to get a good picture of packet activity by listening on these digital-mode bands and seeing what is going on. (A spectrum analyzer or software receiver may help you identify activity visually and allow for faster tuning to frequencies of interest.)
I think most of the packet activity on 70cm and higher bands is point-to-point or "backbone" links between larger sites (similar to a trunked repeater system). This might be due to range issues (APRS uses 2m almost exclusively, if I recall correctly). I have not seen any packet activity in my region (southern Ontario) on any of the higher bands so I can't comment directly on whether packet is really being used on these bands, and if so for what purpose.