Welcome! It's very common that Jeepers sell their hardtops and use softtops. Also very common to see jeeps with aftermarket tops. Matter of fact, most have aftermarket soft tops such as Besttop or OEM top. In the end, you may need to purchase all three panels for your jeep or find someone who is selling the back panel on the forum.
Note: It's a Jeep, not a car. Posters will remind you of that.