Thanks Dowdstree.
It's not quite as simple to track down as I hoped!
I gather that Lord Bankton had a seat/pew at Tron Kirk, but it doesn't look like there was a graveyard there.
I visited Canongate graveyard last year, and I don't recall seeing any headstone or tomb for Lord Bankton. But I could have missed it as it wasn't on my radar at the time.