Exactly how I see it (a spare) and I've already used the TouchID so much that $179 doesn't seem like a lot for how awesome the keyboard is. Plus, I was able to get the purple color.
How I did it? I opened a chat with support, they said that the only way to handle it was to be over the phone. On the phone, I was told the only way to get it was to pay full price for it. It was handled through AppleSupport as a repair/"request for replacement part". Tech support had to keep putting me on hold to get all the info from whichever other department they were speaking with. I don't know if it matters, but I did pay for AppleCare+ for the iMac. I don't know if that came into play though. I was so happy to be able to buy it, I didn't ask questions :) I saw a lot of the websites that said it couldn't be purchased, so I wasn't optimistic when I called. Basically just said "take my money before you change your mind!" LOL