> Amazon won't deliver one to me for at least six days at the earliest, based on their rural delivery estimate.

That sounds like an Amazon problem. For 40 USD, yubico.com says that it will deliver a shipment on the next business day to this rather rural house I see in the middle of Foothills Road in Newman Lake, Washington.

Also:

> Replacing a key is basically impossible.

If you know that getting next-day delivery is dreadfully difficult, then order a handful to have as spares. "If you can reasonably afford it, always buy more than one." is solid advice for just about every important thing that you are likely to break or lose.