|I'm not so sure this is a serial connector. All the 9 pin serial connectors I have seen have been D Type plugs. You need to find out exactly what kind of interface this 9 pin DIN expects to be connected to.|
If it is in fact a serial connector getting an adaptor that will take a 9 pin DIN plug is going to be very difficult if not impossible.
Check the pin configuration against this list and see if anything looks like it. If it were a six pin DIN plug then it would be a simple PS/2 connector.
or is the plug like this: