I actually would be very interested in buying one of the Great Northerns. My wife is from Duluth and her father worked on the railroad and in the steel plant there.
I would be disowned, were I to get rid of one!
But, I believe they can be found on Ebay and I know a large lot was sold at a Julia auction a while back.
Actually, I think they're fairly common, since a huge amount was cancelled (or something, I'm not real sure of the history of it) in 1929 and most of the holders were either bought out or had certificates re-issued after GN did a bunch of buyouts in 1927-30.
As I said, my G-fathers life's fortunes were made with the GN and even today, we continue to receive dividends from BNSF, based upon his investments back then.
He was a smart man, even if he was French-Canadian by birth and US by his mother.
(Hey, that sounds kinda like Ted Cruz.)