Can't unlock SIM with unoffical ROM !

I have a Tmobile UK phone running a Cyogen ROM. I want to move to different network (GifGaf), but upon inserting the SIM the phone requires unlocking. I've got the codes for unlocking, but they don't work. After a bit of search it appears that I can only unlock my S4 mini with the official ROM installed which I must admit surprised me.

Therefore does anyone know where I can find an official Tmobile ROM for a UK S4 mini ?