Where can I buy it in 2021?

[WhoKnows_WhoCares]

Yeah, Amazon is a good starting place and usually sells cards, packs, collections and all the other stuff. Ebay is really only good if your after a specific card in my opinion, but give them a search and you might find other things as well. I know of a few online specialists of cards but they will be in English and I'm not overly sure on if they'll ship to you.

A good tip for anybody if you just google Pokemon Card Seller [your country here], you should start to find places to get your hands on cards.

If you are starting out and don't have anything, I recommend finding and getting a Trainers Kit followed by either the League Battle Deck Zacian V or the League Battle Deck Pikachu & Zekrom. That should give you a good starting ground. Everything in them is in standard as of the date of this post, although a several of them will be rotating out of standard when the rotation happens (which is usually in September). I think the Zacian deck will have more in standard than the Pikachu & Zekrom deck, but I cant recall exactly what's in each so I couldn't give you exact numbers.