The best way to search out internships is go directly to the source. Make a list of companies you would like to work for or look up to and go directly to the job/internship section on their websites as they usually have information on this.
Take a look for internships listed at Studio 32. Of course, consider what production company you would like to work for, and write a list. An excellent source of info would be IMDBPro. It does cost $19.95 a month, but it's worthwhile to study the industry that way. Best wishes.