@8unni3s,
Hi 8unni3s
I'm afraid I have no experience with this unfortunate problem. But I would suggest you search for possible solutions using a google search. For example, type "how to discover an unknown biological parent" or some phrase such as that into the google search box. Then go through the "hits" that come up.
I doubt it will be easy and expect it will take you some investment of time but if your mom won't help out you'll have to turn to other means.
I have little doubt your particular problem is more common than most of us know. Perhaps you might set to this project in a manner that can help others like you in the future. You could document what you do in this search to find him - the attempts that don't work out and those that actually get you close to solving it - and then write up your account as a book.
I wish you the very best of luck. And perhaps someone here might have experience to help you along. But if not, don't let that stop you.