Hi
I suggest the following: Connect the "external" as usual to the "gov agency". After the download is done, just disconnect the network cable, connect to the internal Hub / switch and upload to your "internal processor". with this you will not violate (to my knowledge) and legal binding of your contract. (normally, transfer of data by electronic means will be permitted, provided security precautions are taken care of). For this particular folder, please change the permissions of access to "external" and "internal" users.

As per the internal connectivity is concerned, you may have to connect a simple proxy machine with two NICs, one having "external" IP address and the other "internal IP". If you think that this is not possible for economic, simple sol etc., you can change the IP address of the machine without rebooting.

Good luck
Nadiminti