While it isn’t brand guidelines per se, internal Health NZ | Te Whatu Ora folk can access all the relevant files here:
https://hauoraaotearoa.sharepoint.com/sites/Intranet/SitePages/Comms-media-branding.aspx
https://hauoraaotearoa.sharepoint.com/sites/Intranet/SitePages/Brand-assets-and-templates.aspx
However, that won’t help you very much!
This email address might prove helpful for you (is on that page):
creative@health.govt.nz
creative@tewhatuora.govt.nz