@feldwebel2012 Any Nano, a genuine Arduino or a clone will work. I recommend buying one with a genuine Atmel ATmega328p microprocessor and you would also want it to have the bootloader already installed.
I have used these brands: HiLetGo, Geekcreit and Sainsmart but others should work just as well. They are ~$3 from places like Banggood but you can get them faster from Amazon or a local ebay seller for around $6.
This was just the first one to come up on Amazon with Prime selected (example) https://www.amazon.com/Arduino-Board-ATmega328P-Micro-Controller-Projects/dp/B07X5VQ9XH/ref=sr_1_6?keywords=arduino+nano&qid=1575719510&sr=8-6