First you should ask if it exists in digital form at all...

Right, but i think it does actually. Here is an artwork with it:

http://www.surplusurplusurplus.com

Here's another example:

Have you tried to ask the poster’s designer?
http://www.surplusurplusurplus.com/index.php?Page=Contacts

Shame about the ‘ which should have been a ’ in the first poster. Damn you, autocorrect.

Case solved. It will be available next year via Colophon.

It’s available now.
http://www.colophon-foundry.org/fonts/lydia/about-font