Barrett, I think the soldier who made it first to the crashed Triplane was an Aussie...
As to the seat-- there is a picture of it in Kilduff's THE ILLUSTRATED RED BARON, on page 124. The caption is as follows:
"The seat of Fokker Dr.-1 425/17 was awarded as a trophy to Captain A.
Roy Brown, the putative victor over Richthofen. In turn, he presented it to the Royal Canadian Military Institute at Toronto..."
It was even suggested that MvR was machine-gunned in the back, but this was actually a row of rivets on the seat back, visible because the fabric cushion had been removed.