Returning to the original question ...

I visited the Isle of Wight's only vehicle scrapyard and I was in luck. They only had one minibus, an ancient LDV, but it had just the kind of handle I was looking for.
So then it was a question of fitting it - I thought maybe I could put nutserts into the door pillar, but then realised there were already some that had held a bulkhead back when it was a real van. Also, a handle just screwed to nutserts wouldn't be very strong but I reckoned a piece of 4mm steel attached to 4 of them would spread the load enough.
So here it is:

I'll probably take it off and paint the steel at some point, but I just needed to get it in and functional for now.
Cheers, Rick