http://dbwbp.com/synthbin
Also looking for v0 and v2. I know v4 exists but I do not need that, thank you anyway.

Here are the serial numbers which match each ROM version:
OS 0 - Factory supplied with Ser.no. 360100~393899.
OS 1.0 - Resolves problem with losing tracks while in write-mode. Ser.no. 403900 and up.
In the unlikely scenario that anyone has any other version (v3?) then I would absolutely welcome them.
If it matters, this is for development purposes and not to fix my (non-existent) machine. Nor is it for profit. In other words, it's pro bono for the community.