For some reason i cannot really find online Mann or Mahl filters but there are plenty of BECK-ARNLEYs.
Are they essentially the same as stock ones or, well, not so good?

Wow, brings back some memories. I "retired" 10 years ago as a District Manager from BeckArnley/Worldparts (as it was called at the time). Frequently, they used OE suppliers for the European parts (such as Mann). They have always specialized in "import" car parts only and were excellent quality back when I was there.

I would use that brand without reservation.

did you try suncoast parts???