What is your host ? The driver depends on the diode on one side and host/battery on the other side.
Actually any driver will do as long you have the right set resistor for that driver.
My 685nm laser is build in a C6 host with the DX buck driver running on one 18650 cell.
If you are stuck you could try modding a moh linear. I realise it will waste a lot of power as heat, but at 50 mA it shouldn't be too bad. I once ran a mits 500 with Vf of, IIRC, around 2 or 2.3 V off a moh linear @ 1.35 A. Wasnt ideal but it worked. :beer:
Edit: BTW it also worked with only 1 cell, as the Vf of the diode was so low.