I use this exactly this for D1.
If you can not buy from this source search for “RoHm 0.5A/20V Schottky SOD-323, RB551V-30 TE17” on eBay or Aliexpress.
For C1 I use a 10uF cap size 0805.
I would recommend to first try to build a single cell verson of this driver and than modify another for two cells. Firmware can be a little tricky for two cell drivers.
Another option I use in most of my single cell lights is this FET+1 driver. It is more efficent in the low modes and you can use the awesome blf-a6 firmware from toykeeper ~toykeeper/flashlight-firmware/trunk : files for revision 250