This was 2927mm, in December 1995 at the Cropp River, Waterfall gauge. This site holds most of NZ's rainfall records for various durations.

The daily values:

1   59
2   81
3   11.5
4   0
5   44
6   16
7   15.5
8   91.5
9   3
10   0
11   210
12   395.5
13   531.5
14   0
15   0
16   0
17   115
18   2.5
19   0
20   0
21   114
22   371.5
23   62.5
24   48.5
25   40
26   5
27   111
28   518.5
29   13
30   66.5
31   0

The next "best" effort was 2845mm at North Egmont, October 1998.