There are a few museums of military vehicles that are owned by wealthy guys that just like tanks. One comes to mind up in the state of Wyoming in a little town of Dubois that has a population of less than 1000 people. There is also a an outfit west of me near Uvalde, Texas on the OX ranch where you can go drive tanks. Their web site is DriveTanks.com. They have a Sherman tank, a Soviet T34-85 tank, and a British Scorpion tank. They also do live fire demonstrations with live shells.
When I was in the Army National Guard back in the 80s & early 90s, My company's air traffic control platoon brought a mobile anti aircraft gun back from Iraq after Desert Storm. They just loaded it up with their radar equipment for the trip back. There were no tanks left there that were worth bringing back as souvenirs.
That old German A7V, the Mephisto, was the only one of the 20 operational tanks of the German Empire to survive. It fell down into a shell crater from an artillery round that went off in front of it and was abandoned by the crew. They either set off a charge off inside of it or it was hit by some sort of explosive projectile that damaged part of the roof top and frame structure. It set there in the crater for months after. It was a joint British and Australian recovery in a night mission to retrieve it under enemy fire. They did study it after recovery but it didn't take long to do that since they had other captured A7Vs. The Germans had more captured British Mark IV tanks than they had of their own but it was worth a look. The main gun used was a captured 57mm type so it didn't pack a big punch for it's size. It was moved to London after the recovery. A lot of graffiti was painted on it by soldiers that were exposed to it. The Australian Forces did the Lions share of the retrieval on it so after discussions on the matter in London it was loaded on the SS Armagh at Tilbury on 2 April 1919 for it's trip to Australia. While it was still at sea, there were problems deciding on where it would end up after reaching it's destination. The history of it was a lot more interesting than it's short service life in the Imperial German Army.