Hey, fellow Kiwi here. Try Tower, their premium contents policy covers up to 10k standard, but you can specify up to $14k no problem just have to ring them, replacement value too
my friend has recently got builder risk insurancein kiwi and was satisfied with their service, he also wanted to cover his bike as well and got a good coverage rate. there are many companies in newzealand who can provide you good rates
I'm with AMI and just called them, added an extra $13k onto my contents and they dont even ask to specify or separately list the ebike on the policy. Only cost me $4.30 per month extra
We added my bike to our home and contents with State insurance. From memory it's an extra $200 per year-ish. The bike lives inside and we have deadlocks etc.