This may be all the information you have already, but according to the HSNO Your Practical Guidelines, "If your workplace keeps spare acetylene and oxygen cylinders, store
them separately to minimise the potential for harm if an incident involving a set
of cylinders occurs", and yes it seems they should be stored at least 3m away from each other. These guidelines from Boc Gas are useful, particularly page 24, https://www.boc-gas.co.nz/en/legacy/attachment?files=tcm:U435-82369,tcm:435-82369,tcm:35-82369.

Thanks @Lucille N - yes this one of sources I found for the suggested good practice of 3m.
I still can't find any legal requirement for separation of small volumes.

NZS4781-1973 COP for Safety in Welding and Cutting provides guidance on the use and storage of cylinders.
3.2.4.1 states Oxygen cylinders shall not be stored near highly combustible material......acetylene or other fuel-gas cylinders....
3.2.4.3 Oxygen cylinders in storage shall be separated from fuel-gas cylinders or combustible materials.... a minimum distance of 6m or by a fire resisting barrier at least 2m high having a fire resistance rating of at least 1/2 hour.
The standard is priced around $45 and has a wealth of cylinder use and storage information.

Thanks Denise - some good information in there, but I do find it a shame that NZ Standards seem to never be kept up to date. I'm trying to find a copy of AS4332 (or AS4289) which has some details regarding minor stores of gas cylinders (which I think is one of the origins of the 3m rule). At least the Australian standard was updated this century (the NZ standard is close to been able to claim itself as an antique!).

Agreed, I note the American Welding Society Health and Safety related Z49.1 standard it was based on is now dated 2012 and is available free from the American Welding Society. It appears the separation distance in this updated document refers to 20 feet or 6.1m see 10.8.2.3