I too am adopted and tried for years to find my BM. Eventually I used an agency and they were great.
They wrote to her, a sort of cryptic note, stating xx (giving my birth name) would like to get in touch. This gave her the option of covering if she hadn's told her husband about me.
However, she had told her husband and wrote back saying she was sorry, but the past should say in the past and she hoped I'd had a happy life and she'd see me in heaven.
I thought I was prepared for the rejection, but I wasn't. It was really upsetting as it felt like she'd rejected me twice.
Not to be deterred though, I found I had a half-sister who was in her 40s. I wrote to her telling her the whole story.
She phoned me the next day saying she hadn't known anything about me and she was shocked her mum had never said a thing.
She took it upon herself to bring her mum round and we eventually met up. It was really lovely but they live so far from me it was like communicating with strangers., i.e. what's the weather like etc. We eventually lost touch but I am glad I made the effort and glad I met her as it gave me a sense of knowing who I was iyswim
Good luck and use an intermediary