There probably are some companies out there who do offer internships for free.  However, some of the reasons internships are popular with companies are:

1)  Generally it is the first work experience

2)  Due to this being entry level, the candidate is unaware of the salary base and eager to take whatever is offered--thus a cost savings for the company

3)  The whole experience spawns a loyalty for the early working life of the employee, which benefits the company.

You may want to check the job boards at a local college.  This is where most internship positions are posted.  Sometimes, they will tell you the name of the company, even if you are not alumni.  Another way is to search the largest companies in your area.  They are more likely to have internship programs.  As you are a graduate of a college or university, check their alumni information.

The best advise I can give you is NOT to work for free. You lose pension and 401(k) type contributory benefits that you will use in the future, as well as other benefits such as employer paid life insurance, medical, etc.

Best of luck!