Well, using an ordinary 4mm bolt has worked so far. Though I do notice that it doesn’t quite fit entirely too well and has a tendency to give off some worrying rattling. I might consider trying to get one with a nut that is also maybe a little longer too. Still, in the event it snaps I’ve got plenty more. Just have to hope it doesn’t slip into the frame ^_^;;
Still haven’t had too much luck getting the pin out, though perhaps I need something to give my pliers good grip like a rubber band.
In retrospect, I perhaps wonder if it was maybe the swaying action I usually do on my bike that snapped the pin. Because I’m fairly sure I had the bolts on fairly tight otherwise.
I haven’t received a reply from the Australian distributor, but I’m not too fussed. I’m just glad that I’m at just the right height for the seat to cover both holes.