Sophia,
Tomy are actually advising you that you shouldn't be using the UK baby alarm at all in NZ.
If you still want to, then there are a couple of options:-
1. Use a plug adapter, for example
Korjo Adapter which is available from many outlets e.g. DSE, Bunnings, Mitre 10 etc. This specific one is very good quality and will be useful for many years (for other products).
2. Replacement adapter, for example
DC adapter which can be used instead of the original. Note: You need to check with the store that this has the correct plug and voltage supply i.e. take your current one into the shop and ask them for a replacement.
3. Buy a replacment product, for example
Tomy Link Baby Alarm. This is very limited stock but might be suitable and not much more expensive than just buying just the replacement adapter?
Personally, I would just go with option 1.
Ian