Where to buy

https://www.st.com/

https://www.microchip.com/en-us/products/microcontrollers-and-microprocessors

https://www.ti.com/microcontrollers-mcus-processors/overview.html

https://www.arduino.cc/

https://www.amazon.com/s?k=stm32+103&crid=3J6PP6N2QIPS3&sprefix=stm32+103%2Caps%2C344&ref=nb_sb_noss

https://www.amazon.com/PIC-Microcontroller/s?k=PIC+Microcontroller

https://www.amazon.com/s?k=TI+Microcontroller&crid=11374KKDLSX5A&sprefix=ti+microcontroller%2Caps%2C243&ref=nb_sb_noss_1

https://www.amazon.com/s?k=arduino&crid=HS2SPTP474CE&sprefix=arduino%2Caps%2C272&ref=nb_sb_ss_ts-doa-p_1_7