Actually, few had a 20" front wheel, but one or two did. One even had a 16" front wheel with a 24" in the back. Anyway...
Schwinn Manta Ray
Huffy Super Stock
Sears Spyder 24"
Murray Eliminator IV (I believe)
Those are off the top of my head. I'm on my phone, but I you want to click the links on my sig below you'll find a 24" Super Stock, and Sears Spyder. You'll also find a couple 26" customs muscle bikes I've built. (Monster Ray, Super Slingshot)
What are you after, or why? Maybe we can help you find it.