Gatito, I don't think that's what he needs.
MAC addresses are local to your network. This means they have no significance outside of it (on the Internet, for example). As a matter of fact, they are not even sent out with your Internet traffic. So trying to find the MAC address of a router tha you are not directly connected to is, for all intents and purposes, impossible.
Assume that everything I say is or could be a lie.