Not sure what they look like, but maybe you can use the door pin and bushings that's used on the front doors.
He may not have a local Chevy dealer since he’s in the UK.Here's a link that you might try: Wholesale GM Parts Direct To Your Door | GM Parts Online You should be able to look up the part number, which you could then use to Google search the pins. You could also check with the local Chevy dealer's parts department for the part number.