I’ve done Schalke (v Dortmund), we were there two days before the game without tickets. Went up the ground first day we got there, they had open training on at pitches adjacent to the Veltins. We thought they would be on general sale still....it was a Derby so of course they weren’t. Ticket office told us, unless you were a member they couldn’t do over the counter sales anyway for any game.
We ended up buying tickets from some sound lads the night before the game but know we were lucky. Gelsemkirchen is also dead, nothing there at all. We went thing it would be easy, but it isn’t......stupid foreigners strolling over and thinking you can just get a ticket! It ain’t Anfield. If you want certainty, go for a package with a pen agency that gives you guaranteed match tickets before you set off. If not, take a flyer and do your best to pick up in the town....try the Club shop by the main square, it’s about six stops on the train to the ground from there... the lads in there will try and help, like they did us. All the best