I've read somewhere you had to play a complete round on speacial force to be able to unlock it. I join a game with bots, completed the round and played the next one. But still i can't see it in the weapon unlock screen

Dear Tatarr,

you need to play on an online Ranked Special Forces Server, like ours. You can join us when we play during the evenings, it's a lot of fun! Make sure to join our Discord if you're not in there already; if you are unfamiliar just refer to our easy Discord Guidelines!!

These are the unlocks guidenlines by BF2Hub by the way: bf2hub.com/unlocks.
Regards, Staff Officer S_h_a_r_k_93