Looking for my adopted half sister

I don't have much information to go on but I'm trying everywhere I can think of to find my half sister. She was born in or around 1973 I believe in Vancouver, BC or possibly another part of BC. Her birth name was Natalie. Birth Mother's name was Mary Gay McGregor (born in 1954) Birth Father's name was Rick Finley (Findlay, Finlay, not sure of the spelling or if that is even his last name). As far as I know Natalie has tried contacting our Mom years ago and our Mom didn't want anything to do with her (this is what I hear). I desperately want to find her as she is my sister. If anyone has any information please post or contact me privately. Thank you.