Yale can't help because they don't sell my alarm anymore apparently

but I'm looking for a replacement for my control panel battery for my Yale alarm as it fails to hold a charge for more that 15 minutes or so (and not the quoted 8 hours approx).
On top of that, the alarm will not arm for approx 15 hours as the battery charges (force arm does not work) - rubbish I know.
Does anyone know where I can get a spare 7.2V 600mAh Ni-Cd replacement?
I've googled the P/N GP60AAS6YMX until my fingers have bled

to no avail / contacted Yale / seached the forum etc.
Thanks in advance and happy new year all.