Tony is absolutely correct. Volume lX of the Postage Stamps of New Zealand (Pub. by the Royal Philatelic Society of New Zealand) is an excellent source of information on the subject of Postal Stationery.
The information you require is on pages 125-6.
There are two types of card. The first (issued in 1935) has the lines of the instruction "IF USED......" 1Â½mm apart. The second type (recorded from 1938) has the lines just Â½mm apart. The second type is much scarcer.
There are 9 different adverts recorded. Details from Vol lX below:-
Hope this helps.