Most Scuba bottles in New Zealand have a LAB number but there is an exception when it is not required. If a scuba bottle has been manufactured to ISO standards, has the correct “UN” markings and an import certificate has been issued by an authorised inspector it can be filled in New Zealand by any dive shop.
You can verify these facts by referring to:
Part 15.3 of the HSWA Haz Subs regulations states the regulations relating to Precomissioning of cylinders (LAB numbers) do not appy to dive bottles marked under part 188.8.131.52 of the UN model regulations. http://www.legislation.govt.nz/regulation/public/2017/0131/25.0/DLM7310579.html
Page 116 of the 2013 Guide to gasses states dive bottles marked in accordance with part 184.108.40.206 of the UNRTDG 2011 once issued a import certificate can be legally filled in New Zealand. https://worksafe.govt.nz/topic-and-industry/hazardous-substances/guidance/substances/gases-under-pressure/