I think I'm going to have some good luck on this message board, from all the folks researching McKellars in Argyll!
My grandfather was Malcolm (Caldy) McKellar, b. abt. 1913, d. abt. 1969. He lived in Cairnbaan & was worked onsome water works (Crinan Canal?) nearby. He was not married to my grandmother & he never did marry. He had a sister, Catherine, who married a Turner. Since I never met the man & illegitimate births were not readily talked about, I know no more. I'm sure someone out there does. Thankyou. I am looking forward to finding some lost family.