Silver currency was introduced in New Zealand in 1933, with the same specifications as the corresponding denominations in the United Kingdom. The New Zealand shilling had identical measurements to the United Kingdom Shilling. Its composition (before it was debased in 1947) was 50% silver, 40% copper, 5% zinc and 5% nickel. 1937 was the first year of issue for King George VI.
With the introduction of decimal currency on 10 July 1967, the newly introduced 10 cents denomination was equal to one shilling; the two coins were identical in size and shillings remained in circulation (and legal tender) in parallel with the new coins until they were both demonetised in 2006, when a smaller ten cents coin was introduced instead.
Thus, one shilling coins issued in 1937 could have circulated for 69 years before they were demonetised on 31 October 2006 (although in practice people would have hoarded them because of their silver content and taken them out of circulation much earlier). | 
Search for New Zealand: Shilling 1937 on eBay 