I tried every possible screw which came with my case - no luck. Unfortunately in Poland it is hard to find a store which offers screws for this fan. I will try to contact CM HQ in Poland but as far as I know they don't tend to reply.
I thought about this "plastic zips" or whatever it's called to mount the fan but I'd prefer screws.
Maybe I didn't get all the screws which I should... The long screws which are used to mount the 200mm fan almost go through the holes in case. I tried the medium lenght ones - the same problem. I didn't find screws which are "fat" enough to hold the fan.