Hardware

I'm trying to find a device to sync NTP from but I have several distinct requirements:
-Must be battery powered (or capable of keeping time when not plugged into power)
-Must be able to sync to/from several other devices of the same kind
-Must maintain less than 1ms sync between disconnected devices to include drift
-Must be able to travel (needs to fit in a pelican case)
-Must support NTP
**BONUS** Would be great if supported IRIG-b!

This solution will be used to sync time between several systems spanning 4 time zones. Utilizing internet sourced NTP servers cannot maintain difference requirements. The budget is healthy. Would be nice to have some sort of accreditation or certification. Any recommendations are appreciated! Thanks