This is a very DIY thing, if you want to source the parts yourself and assemble it and flash it yourself. It takes some outside research or prior knowledge to figure out what substitutions can be made (like, if you can't find a X7R 16v capacitor, should you look for a X5R 16v or a X7R 10v?).
This is a direct drive driver. It's job is to connect the cell/cells direct to the LED/LEDs as efficiently as possible, there is no regulation or limiting or anything else of any kind. You can use combos other than one cell/one LED, as long as the LEDs can survive being connected direct to your power source with no driver inbetween... 3 XML2s in series with 3 series 18650s, 1 MTG2 with 2 series cells, etc. Higher input voltages will require a Zener diode to limit voltage supplied to the MCU to 6v or less.
Here's the current parts list for the most recent board revision: http://www.digikey.com/short/dq403 Even if you do not live someplace where shipping from Digikey is reasonable, USE THAT LIST to get the part numbers and/or specs of parts used!
The board: https://oshpark.com/shared_projects/IHvO85FY
Capacitor on this latest version has been relocated from the original Nanjg spot between pin 8 & ground, to between B+ & ground. Same parts used, the pads just connect to somewhere different. (This is because with the 'hard' load the MCU's PWM pin has to drive (the big beefy FET instead of dinky little 7135s) the original Nanjg layout of capacitor & diode created a boost circuit, and MCU input voltage would rise above the shutdown point and create unreliable mode changing. The old gate resistor was a clumsy patch that eased the load and reduced (but did not eliminate) the voltage boosting. The cap relocation totally eliminated it, and the MCU now runs at battery voltage (minus the drop through the diode), as it should. If you'd like to see the investigation that discovered this, click here: https://budgetlightforum.com/t/-/27485)
U1 - Atmel ATtiny13A SSU (or SSH, interchangeable)
FET - N-channel MOSFET, logic-level gate, gate threshold as low as possible (most will be around or just under 1v), 'total gate charge' (Qg) less than 40nC, lowest possible Rds(on)at 4.5v
D1 - SOD-323 Schottky diode
C1 - 0805 ceramic capacitor, 10uF 16V 10% X7R
R1 - 0805 resistor, 19.1K 1%
R2 - 0805 resistor, 4.7K 1% (tip: the 4.7K resistor is the one that connects to ground on one end; the 19.1K is the one that does not have one end connected to ground)
'2', '3', '4' - these numbers correspond to the 'stars' from the original Nanjg board, NOT the MCU pins. For instance, 'star 4' is on MCU pin 2, and the official name for pin 2 is 'PB3'. Confused yet?
'A' - bridge the two pads to ground pin 2 when using some firmwares; install 1uF 0805 ceramic cap if using an off-time firmware; if using momentary firmware, connect one side of your switch to the inner pad.
'B' - return feed from the 19.1K/4.7K voltage divider
'C' - power feed to the MCU, from the polarity protection diode