There are two main parts to a MAC address: the first three octets are the Organizationally Unique Identifier (OUI), and the last three octets are Network Interface Controller-specific (NIC-specific). The OUI is important here because it uniquely identifies a manufacturer. The manufacturer will purchase an OUI from the IEEE Registration Authority and then hardcode it into their devices in-factory. This is not a secret – it's public information, encoded into all the devices a particular manufacturer makes. A simple Google search for Apple OUI helps us narrow it down, though you can also pull up the IEEE Registration Authority website directly. We quickly find out that 00:21:e9 belongs to Apple, so we can try to spoof a random NIC address with that (for example, 00:21:e9:d2:11:ac).

But again, vendors are already well aware of the fact that MAC addresses are not reliable for filtering, so they're likely going to look for more indicators.