I have seen secure sticks, but they are lower capacity and a LOT pricier. These are of the sort where after a certain number of login attempts, the secure data is scrambled, and the stick melts down.
I suspect that procurement cycles would keep these things out of government programs, except as personal storage in IT type situations. My current project (network server on military aircraft) is just shipping, and secure storage is locked into 2 GB PCMCIA cards. USB sticks are explicitly locked out, even though the USB port is available.