For several reasons, including lack of resource and inherent ambiguity, not all names in the NZETC are marked-up. This means that finding all references to a topic often involves searching. Search for John G. A. Castle as: "John G. A. Castle". Additional references are often found by searching for just the main name of the topic (the surname in the case of people).
The following collections may have holdings relevant to "John G. A. Castle":
- Dictionary of New Zealand Biography, which has entries for many prominent New Zealanders.
- Archives New Zealand, which has collections of maps, plans and posters; immigration passenger lists; and probate records.
- National Library of New Zealand, which has extensive collections of published material.
- Auckland War Memorial Museum, which has extensive holdings on the Auckland region and New Zealand military history.
- Museum of New Zealand Te Papa Tongarewa, which has strong holdings in Tāonga Māori, biological holotypes and New Zealand art.
- nzhistory.net.nz, from the History Group of the Ministry for Culture and Heritage.