I'd be real surprised if anyone makes an 8-track car stereo anymore.
You'd probably have to buy a used pull on eBay or your local junkyard. Since 8-track players are so obsolete, it wouldn't really matter what make or model you got since unless your car is over 20 years old, it's a sure bet they didn't make one for your car. Then you'd have the problem of wiring, assuming it fit the open hole in your dash at all.
If it fit, making your own wiring harness wouldn't be all that hard assuming you're not colorblind and can deal with a little trial and error.
The whole thing might make for a fun Sunday afternoon project. I always do all my car stereo stuff myself. Taking it in to a place like Magnolia HiFi or Car Toys is such a rip. They always want like $30 or $40 just for a f*cking wiring harness. We're talking FOUR INCHES OF WIRE and a PLASTIC CONNECTOR here, folks. C'mon! And that's on top of like a $70 labor bill, plus anything else they can dream up to charge you for.
When I was learning to drive, in my parent's '74 Cadillac Deville (or Seville?), the 8 track player was still going strong and I listened to them all the time. Of course, I wanted to listen to cassettes, too, so I bought an 8-track---to---cassette convertor from Radio Shack. I was stoked! So were my friends! Unfortunately, the dashboard had an overhang on it and it prevented the bulky convertor from being inserted into the 8-track slot! Crap!
I reluctantly returned the convertor to Radio Shack.
The 8-track player eventually broke, after 25+ years of faithful service.
In the car
prior, which was a '66 Chrysler with fins, we had a glorious AM RADIO. At some point, my parents went crazy and added an FM tuner as well! The funny thing is that the FM tuner was mounted underneath the dashboard... at shin-level. To change channels, you had to streeeeeeeetch your arms and lean away from the steering wheel.
Good times.