Steve, the database for the Historic Iris Preservation Society shows one member has 'Emma Law' in their holdings. According to the database there is no known retail source.
I would recommend going to the HIPS website, www.historiciris.org, then click on 'Contact' (upper right on the menu bar) and send an e-mail inquiry. That e-mail will go to the individual who maintains the database (I think) and he may be able to put you in contact with the member who has the iris you're looking for.
If that doesn't work for you, please send me a private message and I'll see what I can do to help.
Randy Smith
By the way, it can be difficult, but not impossible, to import rhizomes from the U.S. to New Zealand. HIPS has contacts in many countries, including New Zealand and may know of a local source. Again, try the 'Contact' e-mail first. Let me know if you need more help.