Southern Trust became the sponsor for the National League when I think Ansett folded. In later times NZ Community Trust was involved.
Bluebird was solely a regional league sponsor - used to sponsor all three. Northern League also had Country Foods (of yoghurt fame) and Hertz sponsored Central and Southern - lots of van hire in both these leagues.
As far as clubs go then there was DB Spats Wellington (Spats a nightclub owned by Ray Johns) and Miramar also had sponsors by Arena (Ray Johns nightclub) and Pines (restaurant in Houghton Bay). Dunedin City sponsored by 4ZB .Hamilton by Zelos (no idea who they were !). Plenty of others but a lot were one season wonders which i think is why NZFA didn't really like it. The National Mutual / Miramar relationship was I think the longest at 9 years.
for the longest not sure if thats right National Mutal were a long term sponsor but I think Hanimex were involved ion North Shore for longer also the DB one with WDU and then Wellington United was a pretty long one (and very lucrative about $65k a year!) Spats got involved as they sponsored Wellington City and when they merged they got naming rights - DB weren't too happy about it though as Spats only put in about $10k, Ray Johns eventually decamped to Mar when Barrie Truman moved and Arena replaced Spats, DB stuck with Wellington United until the Superclub years
Others I can remember (that haven't been mentioned)
Southmall Manurewa, oh and also Magic Carpets Manurewa - I remember that because I went to a game in 1986 that was DB Spats Wellington City Diamond United v Magic Carpets Manurewa - that long name was definitely more memorable than the game!
Landbase Papatoetoe
4XO were Dunedin City sponsors at one stage
University Cowan
Rolle Hutt Valley United
NZ Permanent Gisborne City