I hadn't even heard of this model until recently when one appeared on Trademe, it closed without a single bid at a start of NZ$38 and was then relisted at NZ$15, this time it went for NZ$88.50. The psychology of auctions is beyond my ken.
Anyway I have been driving around the South Island this week while ostensibly attending a conference in Dunedin. I have lost track of the antique shops and secondhand stores I have tried, all to no avail. Finally today, on my last day, I dropped into an antique shop in Christchurch and found this set, again a 77. It still has the original sac and Duro 58 nib. It's quite a large pen, very similar to the 58 but I think slightly longer at c13.5cm. I look forward to cleaning it up and adding it to my collection.
Photos not up to much - away from home!