There is an ISBN URN namespace, but I don't know whether anyone maps it to anything. https://www.iana.org/assignments/urn-formal/isbn https://www.iana.org/assig

There is an ISBN URN namespace, but I don't know whether anyone maps it to anything. https://www.iana.org/assignments/urn-formal/isbn https://www.iana.org/assignments/urn-formal/isbn