How Do I Find My Siblings Who Were Also Adopted ?

My biological mother had 5 children, including myself. She gave 3 of us up for adoption. I would like to find my brother and sister who were also given up for adoption without having to involve our biological mother since I have no desire to know anything about her. I'd like to do the research on my own and I can't afford to pay those services that have your information in their database. Any ideas as to where I can start? Social services gave me a 1 page brief without much information.