I'm from Canada and bought them before the update. All the stores sold them when they first came out and than people stopped buying them. The cards took up too much space and customers stole them. For Series 4 most of the stores went to online only purchases or put them on sale to get rid of them. After the update they sold out. Customers were trying to get something that the stores weren't interested in selling anymore.
I bought some of mine from amazon and ebay Canada while the prices were still low. $2 for one card was a good deal when I was close to completing my collection. I also used online local sites. One I used was Kijiji and met the person at a local coffee shop. We traded and I bought cards from her. Those usually list what cards they have and how much. Buying the cards separate is a better way to get them. A package can have repeats.
I've seen some posts where players bought homemade amiibo cards from Esty. Posters said they worked when they scanned the amiibo card. The price is lower than the cards.
My local EbGames had the 3 amiibo figures set for $5.99 a few days ago. Just looked on Walmart Canada online and they are selling one card for $19. Walmart stores don't have them anymore. Best Buy stopped selling them.