I've scaled up a lego technic pin to fit duplo technic parts found on aliexpress. I couldn't find any existing pins for duplo sized parts so used the dimensions from ortwins duplo models to create this file.

I have tried printing both vertical and horizontal(with supports) and my advice is to print horizontal. As you can see in the 3rd picture I have put the pins under some serious stress tests and only the vertical printed pins have broken so far. It seems the vertical layer lines run along some of the high stress points.

A single pin can handle a fair bit of weight as you can see in the image but if you put 3 next to each other I've been able to get it to support my own weight. You can see a few extra photos of them in action in the photos of my 2x4 duplo technic brick https://www.thingiverse.com/thing:6412318