I've got a RetroSound 4" x 8" dual coil speaker brand new in the box that's left over from my recent finnie restoration. I was going to retrofit a modern radio in the car until I got a deal on an old Becker (my first choice, of course.) So now I've got this brand new speaker sitting around in the box collecting dust. $100 new, I'll let it go shipped anywhere in the CONUS for $70. Here's a link to the specs and I've posted a picture below. Drop me a PM if you've got questions.
https://www.retromanufacturing.com/collections/dash-speakers/products/4x8-inch-ultra-thin-dash-replacement-speaker?variant=31321011150
I've also got one of their retro head units, too, if you're interested.