Where do you find good interns? Start by contacting your local colleges or universities. Many have internship programs. Contact the college to find out their requirements. Some schools require that interns be paid, and all expect you to do some paperwork so the student can earn the proper credits.
To make sure both parties benefit, you must prepare properly. Start by writing down the specific job requirements. Then list what the intern will gain. Remember, this is a learning experience for them.
Once you get inquiries, request resumes and interview the candidates as you would any job seeker. After you hire an intern, remember to train and supervise them. If you're lucky, your intern may turn out to be a great future permanent employee.