Ok, I'm sorry. I can't help you find a "12 port RAID controller."
I'd look for 2 more 4 port RAID cards. You should be about to set up what drive go to what array if you use an 8 port.
But, moving drives from one RAID controller to another, you could loose it all. UNLESS, it is the SAME RAID controller (i.e. Intel chipset).
I think they went overboard recording to a RAID 5 array. It would have been much easier to record to one large drive. But hindsight is 20:20.