There are no carriers I'm aware of which will accrue miles for NZ L class ticket. I've got data on TP, LH, UA, US, ET, A3 and OZ in a tool here: http://www.wandr.me/Tools/Frequent_F...g_Options.aspx.

Since you want to earn UA miles the details you need are here: http://www.united.com/CMS/en-US/mark...spx?ItemId=405. Note that for the trans-Tasman flight you won't even earn in T class.