A sperm bank should do a complete semen analysis before banking your sperm. This will not only tell you about the quantity of sperm but the quality as well. The evaluation of the thawed specimen will give you a general idea of the quality of the sperm when you later attempt a pregnancy.
If you are interested in learning more about the minimum quantity of sperm that makes freezing worthwhile, click here.
If you seeking a sperm donation, or are a prospective donor, here is a list of sperm banks by location.