Although Ebay and Amazon are about the only way to buy cards anymore you can get some on etsy for cheap. They sell what's called "fan made" cards. They scan like normal cards but they are ones that they somehow put a computer made chip into. They aren't real but they work like a normal amiibo card and they sell for three or four bucks a peice. It's nice if you don't want to spend 20 bucks on a card to get one of your dreamies.
Honestly, EBay is really easy to get the cards you want. I’ve been buying exclusively from there because I can get the desired card for a reasonable price.