Hey @zoneblue. Thanks again for documenting the unofficial Egmont National Park tracks off Carrington Road at http://www.zoneblue.nz/cms/page.php?view=kiri-track .
This afternoon I finally had an opportunity to go out for a couple of hours and hunt them down, although exploring them will have to wait for another day.
I gave up on the Plymouth Road entrance due to the oppressive private property sign (despite the paper road going straight through the property), but I found the Goodwin Track, both sides of the road, after 30 minutes of hunting up and down from a big space cut out from the side of the road. I stumbled on it after bashing through 30 metres from of scrub, then followed it out to the road to realise there was a giant sign hidden under the road-side scrub.
I couldn't find the Kiri Track entrance but after returning and re-checking I wonder if I was looking slightly too far along the road.