I am trying to get one of these here in Germany but it seems impossible to find one!
If someone has a clue where I might find a foam roller over here, please let me know
Look for a place that sells pool supplies or water toys. In Canada they are called “pool noodles”. Kids play with them in the water. 5’ long x 4" in diameter costs about $5 CDN.
TNT
Alternatively, you could go to a hardware store or plumbing supply store and get a short length of PVC or ABS pipe in 3" diameter or larger. Now you have a roller which will never wear out!
They have those “pool noodles” in every OBI…but I’d recommend a length of plastic tubing as well, the noodles are a little thin and you might want a different feeling. Alternately go to a physiotherapist and ask where to get one.