I am interested in getting Apple Care on a few of my devices

This is primarily a user-to-user support forum; other Apple users like you. See the information in the following for options that may help: AppleCare Products - iPhone - Apple including the excerpt below:

How to buy

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

• • On your device (go to Settings > General > About and choose AppleCare+ Coverage Available)
  • Online (requires you to verify your serial number and run a remote diagnostic)
  • At an Apple Store (inspection of iPhone and proof of purchase are required)
  • By calling 800-275-2273 (requires you to run a remote diagnostic and provide proof of purchase)

If you have owned any of the devices longer than 60 days from date of purchase, you have missed the window of opportunity to add an AppleCare+ plan.