I managed to track down a working version of crpd. It was extracted from a VM image I found, within which it was simply tagged "crpd-custom". I've run the extracted image on my own machine now with docker (via containerlab) and it's working fine. CLI works, SSH and Netconf also.
Hopefully be of use to some people.
To use it in containerlab you just need to load it to your local docker as follows:
# Load the docker image
docker load -i crpd_custom-docker-20.2R1.10.tgz
# Tag it as crpd:latest
docker tag crpd-custom:latest crpd:latest
After which you can define nodes of type 'crpd'
I'm still after a more recent version of cRPD (for EVPN/VXLAN), so if anyone can help there please do!