Bibbie on Family Tree Circles

I am researching my Great Grand Mother Ivy May Collins nee Fitzgerald nee Asher OR Usher said to be born in Christchurch New Zealand c. 1885 (no birth record found).
Said to be Catholic faith, Maori descent and migrated to Queensland Australia c. 1887. Married James Francis Fitzgerald said to be born in Newcastle NSW (no birth record found) in New York City New Year's Eve 1905 (no record found).
They were part of the Flying Fitzgerald Trapeze Act performing with Wirth's Circus.
It is said that 'they' changed their name to Collins due to a contractual agreement with Wirth's and according to Queensland Death Records they are both listed as Fitzgerald.
I have ordered the Death Certificates
I am searching for:
Ivy May Usher birth certificate
James Francis Fitzgerald birth certificate
Marriage Certificate – no record found in New York City
Change of Names Record – no record found
Any ideas on where I should search please.

I am researching my Great Grand Mother Ivy May Collins nee Fitzgerald nee Asher OR Usher said to be born in Christchurch New Zealand c. 1885 (no birth record found).
Said to be Catholic faith, Maori descent and migrated to Queensland Australia c. 1887. Married James Francis Fitzgerald said to be born in Newcastle NSW (no birth record found) in New York City New Year's Eve 1905 (no record found).
They were part of the Flying Fitzgerald Trapeze Act performing with Wirth's Circus.
It is said that 'they' changed their name to Collins due to a contractual agreement with Wirth's and according to Queensland Death Records they are both listed as Fitzgerald.
I have ordered the Death Certificates
I am searching for:
Ivy May Usher birth certificate
James Francis Fitzgerald birth certificate
Marriage Certificate – no record found in New York City
Change of Names Record – no record found
Any ideas on where I should search please.