Hello , I want MAC ID for STM32. How to get that? To whom I should contact regarding this?

[Tesla DeLorean]

You'll need to buy your own MAC address ranges for your own products. The IEEE used to manage this, I'm sure a quick Google would find the place to buy them, and the cost structures.

[Tesla DeLorean]

https://standards.ieee.org/faqs/regauth.html

[Piranha]

For the mentally challenged ones:

https://lmgtfy.com/?q=MAC+address+registration

Alternative for small volume production:

https://www.microchip.com/design-centers/memory/serial-eeprom/mac-address-and-unique-id-eeproms

For local use:

https://en.wikipedia.org/wiki/MAC_address#Universal_vs._local