What goes into ordering a custom module?

What is the process of ordering from Salvation or Jaded Faith, a custom module (ie. one that isn't listed on their sites)?
If I was interested in a particular head they don't have in module format (ex. Elmwood Modena, Straub Cantus), could they make that with information and sound samples online or would I have to provide the actual, physical head?
Any insight would be great.
There were a lot of amps I sold on HC/TGP, that I wish I still had/could find. I'd love to get some of those tones back.

I'd contact either modder to start the conversation. Modules have been modded to replicate recorded tones (eg. the Kore, which I believe was based on a particular STP album). I'm sure it would be possible with some tweaking to match a module to a reference sound sample.