wheel - 7:19 pm on Sep 6, 2011 (gmt 0)
I doubt there's any way to find all the sites they own. You can take some guesses though.
Get the IP address of their main website. Then on Bing, do a search: IP:YYY.YYY.YYY.YYY where yyy.yyy.yyy.yyy is their IP address. That'll give you the websites on that IP. Sometimes you'll see some interesting stuff that way. Also try adding one or subtracting one from the IP, in case they have a range of IP's.
Also check their nameservers.