Hi,
You may get lucky finding an original.. But there's no need. You need an adaptor to provide somewhere between 9 and 12 volts and it should be rated to at least 0.5 amps up to perhaps 1 amp. The output must be DC and with the centre contact of the connector wired as positive. It does not need to be regulated since the cradle has a built in regulator for the DMS. In the UK, Maplins are a good source. Part number XX09K - £9.99 - should be OK if set to 9 or 12 volts.
But do get the polarity right. Most adaptors that are bought separately can be set up positive or negative to the centre contact. My suggestion - once you have it set up, glue things so they can't change.
Me - I had a suitable 9 volt radio adaptor in my junk box already with the correct plug and polarity.
Hope this helps.
