There is another one "Nexia" but it's a zwave plus and you being on the other side of the pond which I believe zwave frequency is different over there so it probably won't work for you.
Nexia Z-Wave Doorbell Sensor, DB100Z - - Amazon.com
www.amazon.com
I am a tinker by nature so there is one thing I can think of at the top of my head that might work for you however I can't promise it will work successful until one test it first.
Get an old or used mechanical doorbell chime.
Dismantle the chime and remove the magnetic coil from it.
Remove the chime kicker from the center of the magnetic coil
Tape the magnetic coil next to the zigbee door sensor on the magnet pick up side.
Attach the wires from the magnetic coil to the doorbell circuity
Ideally, the coil itself should generate enough magnetic to trigger an event in the door sensor when power is applied to it.
Just a theory .... so don't hold me to it ... heck I might even try one myself.