Looking for birth mother in a closed adoption

I'm wanting to search for my birth mother but my adoption was closed. I'm trying my best by going thru a search agency called ALMA registery. My birth mother was an only child and also adopted. She was born in California in the year 1967. She had me at 21 and had 2 other kids born before me. I don't know my birth name because my adoption was closed. So I am still searching not giving up.