I'm not aware that the phrase has ever been a song lyric.
"Fisher" was a company that made undercarriages and auto bodies for various Detroit automakers, they were well known for the quality of their product. So "Body by Fisher" let people know that their automobile body was the best-made available.
"Brains by Mattel," on the other hand, refers to Mattel's well-known 'body' product, Barbie. Therefore, someone that was said to have "body by Fisher, brains by Mattel" was a '10' in the looks department but somewhere around a minus 3 in intelligence.
If it was ever written into a song, it's not one I've ever heard.
It's was in the spoken word section of the song I should be your lover by Harold Melvin and the Bluenotes.
You got a body by? Fisher, but your mind is by Mattel"from (
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