1) First you need a Nema 17 stepper motor. Just use google. This motor is normally used in 3D printers and should be readily available.
You can find small differences in holding torque, steps per revolution and some come with planetary drive (at a much higher price).
Price level somewhere around $16 or about €14, although you can get these cheaper from AliExpress.
You can buy these from Amazon, AliExpress or other online electronics shops and retailers.
2) The second component you need is the L298N motor driver, just google this as well as the same also applies for this driver.
You can pratically buy it anywhere. Pricing around 3 to 5 euros or usd.
3) Last component is an Arduino Nano. It is up to you if you buy the original version or a Chinese clone. I bought the latter and it is operating without any problems whatsoever. A quick search on Google will show you where to buy them. Price is around €5 or about $6 to $7 (for the Chinese clone)
Besides these main components 2 additional items are needed which is wires or jumpercables to connect the components (no soldering needed) and a surplus 12V power supply or 9V battery to power the (stand alone) unit.
All required software is free of charge:
ASCOM Platform > Start with downloading and installing the ASCOM platform
Arduino.cc > Download and install the Arduino software next. This is needed to program or change the code for the Arduino Nano and upload it to the Nano.
Sourceforge – project page > The main project page on Sourceforge.
Sourceforge – files folder > Download the software for the Arduino. Look in the folder “DRIVER BOARDS”. Pick the L298N and download the (M)inimal version.
Sourceforge – files folder > Look in the folder “CODE ASCOM” and download the myFocuserASCOMSetup16xx.exe file. When this is installed, it allows programs such as Sequence Generator Pro or Maxim DL to communicate to the focusser.
These are the minimum software requirements to get everything running. You could optionally also download the test code to check in windows if and how the focusser is moving before installing everything to the focusser on the telescope.