Take a look at this thread: http://stackoverflow.com/questions/1420381/how-can-i-get-the-mac-and-the-ip-address-of-a-connected-client-in-php
Basically you can't get the client MAC address, unless the server and the client are on the same LAN connection.
You can however get the ip from the request
public function store(Request $request)
{
$ip = $request->ip();
}