I was able to add the part to my cart when I first made this post here (and on Reddit). So that's the source of my confusion in regard to Toyota's posts. It appears Newegg fixed whatever happened to me, as I too now get that error.
I apologize to Toyota and the forum if it seemed like I was trolling and/or goading. I was legitimately just asking if anyone knew anything about this part...and since I was able to add it to my cart, Toyota's answers made no sense.
Obviously now, I realize that this is indeed just a system-builder only part, and not like the ones at Best Buy. So that answers my initial question.