You can see what version of defMON you have by looking in the status bar when the program starts up. The version numbers are essentially just date stamps that reflect the day when the program was compiled.
If you got a version of defMON that is not available on this page, feel free to add it here. Nobody will kill you.
The hardware sync interface is available from Scannerboy at the chipmusic.org forum, right here.
The first publicly available version of defMON was the one that was “cracked” by Genesis Project in 2013. You can find it on CSDb. That version differs in some ways from the “ordinary” versions used by people like Goto80, Ilkke, and others.