Yes, unfortunately the pre-installed fans are not available as an option from Corsair. However, I replaced these fans in my case anyway, as I equipped everything with RGB. Accordingly, I decided on the Corsair SP120 RGB Elite (Corsair SP120 RGB Elite (120 mm, 1 x)).

The model of the fans is "RWF0050" there are Ebay offers for them but they are not officially available on the Corsair site. I can imagine that they are not sold individually.