AppleCare+ must be purchased within 60-days of initial purchase/device activation. Eligibility to purchase can be established from iPad Settings. You should see the AppleCare option visible in iPad settings - this usually appearing just below your Name / AppleID.
If not seen, you may see the option to purchase AppleCare here:
Settings > General > About > Coverage
You can also purchase AppleCare for your iPad directly from Apple’s website:
AppleCare Products - Apple
AppleCare+ coverage is only available within the country within which it is purchased.
Generally, you should aim to purchase a device in the country within which you intend to spend most time - as this significantly simplifies the warranty position (and Applecare+) should you ever need to call upon it.