This page does not actually link to an option to purchase Apple Care. How can I do that?

Hello, welcome to the Apple Users Community,

Try this page https://mysupport.apple.com/add-coverage/producttypes?callerId=acs::HT202702

follow the prompts for the device you want to cover.

Best of luck

If you bought it in September it is too late to buy AppleCare, you only have 60 days to purchase AppleCare from the original date of purchase. No there are no exceptions, that ship has sailed and you missed it.

Please refer to https://www.apple.com/support/products/mac/

This clearly states:

How to buy

1. Purchase AppleCare+ with your new Mac.
2. Or buy it within 60 days of your Mac purchase:

• • Online (requires you to verify your serial number and run a remote diagnostic)
  • At an Apple Store (inspection of Mac and proof of purchase are required)
  • By calling 800-275-2273 (requires you to run a remote diagnostic and provide proof of purchase)