shadowmac is a kernel patch for spoofing MAC addresses under Mac OS X. It works even if the device does not support the IOCTL via rewriting the MAC on the wire as packets go out and the reverse when they come in.
You can download it from the following link: https://packetstormsecurity.com/files/download/34597/shadowmac-1.0.tar.gz
Source: https://packetstormsecurity.com/files/34597/shadowmac-1.0.tar.gz.html