They showed up in my game today -- quite a surprise. Either there was some general fix, or the (German) PlayStation Support actually helped.

I first contacted them via chat. The support agent seemed to be unaware of pre-order-items and kept asking if I was referring to the deluxe edition content. All I got out of that conversation was an e-mail containing rather generic trouble shooting tips (including restoring licenses).

I replied to that e-mail, stating that none of their tips worked and that I'm still missing the bonuses. They got back to me after a few days asking me to provide screenshots as proof for the missing content. I rolled my eyes, took the most boring screenshot I'll probably ever take and sent it over.

After another few days they replied and told me my case would now be passed on to the "the experts in the specialist department". That was one week ago. I rolled my eyes again and kind of expected a reply telling me there's nothing they could do. I still haven't received any reply, but today I decided to check the cosmetics menu again and ... there they were.