Hey, I've lurked on this website for a while and was looking at this thread every now and then to see if the cards were available anywhere. Somehow I ended up finding this store in Australia that sells packs (of 3) or boxes of 25 packs, and they do have international shipping, so I thought I'd share it here.
https://thegamecenter.store/products/amiibo-animal-crossing-cards-series-5-cdu-25-packs
While the shipping is expensive, I find it's worth it and these packs are probably the best way to get a complete set (with plenty of extras) if you're a collector like me. I ordered 2 packs and insured shipping for $305 AUD or $228 USD. It seems like a lot but that’s about $1 USD per card, and you can trade or sell the duplicates, which there should be plenty of. (Plus as a collector, I've payed a lot more… I bought the Sanrio pack for $99 a couple years ago which for the time was actually cheap, because it seemed unlikely they'd ever be reprinted…) Also, the reason I got two was because there are 25 packs and 24 special cards, so while it's possible you could get all cards in one box, it's not guaranteed. The only possible downside is that I asked about shipping time, and if you're outside Australia the international shipping can take anywhere from a few days to a couple months. But, if you're looking to complete your collection, I think it's a good option. I hope this helps someone!