http://www.ebay.it/itm/Constant-Current-High-Power-Driver-for-1x1w-LED-Light-Lamp-12V-MR16-/121177849445?pt=LH_DefaultDomain_0&hash=item1c36c33e65
Could it be a good option? Every led would be wired to one of those and 1 Mosfet could switch on/off group of LEDs