I (John Goerzen) have provided a Docker image for NNCP.
See:
https://salsa.debian.org/jgoerzen/docker-nncp
for details.
Links to this note
NNCP lets you securely send files, or request remote execution, between systems. It uses asynchronous communication, so the source and destination need never be online simultaneously. NNCP can route requests via intermediate devices – other NNCP nodes, USB sticks, tapes, radios, phones, cloud services, whatever – leading to a network that is highly resilient and flexible. NNCP makes it much easier to communicate with devices that lack Internet connectivity, or have poor Internet.