How do you get a list of MAC address for products?
Companies that are going to manufacture an Ethernet product for distribution are assigned a block of MAC addresses from the IEEE Registration Authority: IEEE SA - Registration Authority There is a fee.
So if you ship a product where is the best place to store the MAC
It can be part of the program loaded into the product's non-volatile memory at the time of manufacture. That means that every unit that is manufactured must have a different program compiled and loaded into it. Probably not a very good idea for mass production.
Often the MAC address is in a small external EEPROM that is programmed separately before it is soldered onto the board. The application program reads the EEPROM and initializes the Ethernet controller with that value. For moderate production volumes, the EEPROM may be programmed in-circuit on some kind of test fixture at the end of the production line. The EEPROM may have other information also (such as a unique serial number for each unit).
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I'd hate to "randomly" pick a mac that is used by another product(s).
For your own use (or for any device used locally and not released into the wild):
If the second-least significant bit of the first byte of the six-byte MAC address is a '1', it's called "Locally Administered Address." No commercial product should ever have that bit set to 1.
Note that the default MAC used in many Arduino example sketches has its first byte set equal to ASCII 'DE' (or maybe 'de'), so that bit is set, and that address should never be used by any commercial product. (Thus, you sometimes see the six-byte array for the MAC address initialized to something like {0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED};) Get it? "DEADBEEF..." To the chagrin of some of my cowboy relatives, I have also used MAC addresses starting with "BADBEEF..." for personal use products. (Smile when you say that, pardner...)
You only have to make sure that, no two MAC addresses are exactly the same on your own internal network where you are using these things.
Reference: MAC address - Wikipedia
Regards,
Dave