My wording in the post I believe your responding to is off a bit. The 8TB Archine drive is available in internal form factors too. (Specifically ST8000AS0002). Seagate uses the same model by adding an external USB 3 case to it as well, the one I linked to on Amazon.

Local to Seattle, I can only find physical retail stores that stock the USB 3 external variant, and not the internal SATA one. A Frys employee recommended buying it anyhow and cracking the external case, but I'm not willing to do that since I'd lose Seagate's warranty in the process.