score:2
The online portal vacations to go offers this possibility on their custom search. You have the option to choose up to two ports to exclude.
Note that you have to give your particulars to see any results. However, no email confirmation is needed, so using fake particulars should be possible if you are worried about giving out information.
I haven't actually used the website before. There seems to be some mixed opinions on their service quality, ranging from very good to very bad, but as long as you only use it to look up cruises, I don't see much risk involved.