By using the OpenBSD packet filter pf, one can utilize the NAT address pools added into OpenBSD 3.3 to aid in distributed port scanning.
You can download it from the following link: https://packetstormsecurity.com/files/download/31286/openbsdportscan.txt
Source: https://packetstormsecurity.com/files/31286/openbsdportscan.txt.html