According to the Universal Declaration of Human Rights, a child has a "right to association with both biological parents".

http://en.wikipedia.org/wiki/Children%27s_rights

It is unfair of your mother to keep this information from you, but you have little recourse against her unwillingness to tell you the truth. Try asking your mother's doctor - the information is not specifically about her, and has more to do with you. Try asking other family members who were around at the time of your birth. Have you tried looking in the phone book or on the internet for his name?

Sometimes it is better to cut off a poisonous family member, even though it hurts. If in the end the person causes you more harm than good, and obviously she has caused you harm, it is better to be without them.

I wish you luck in your search.