It's actually pretty easy to find one sold exclusively by Amazon.com. The trick is to find where they are the only seller for that item. Here's an example.
I believe it defaults to the "Card and adapter only" option, and for me it lists Amazon.com as the default seller, probably because I have Prime. There are other sellers, with no indication if inventory is commingled, so this is risky. No worries, there's an easy fix, although in this case it costs a few dollars more. Change to "Card w/Reader Bundle". Now Amazon.com is the only seller, so there's no worries about commingling. There are probably other cards with options that cost the same, but this was the very first I found.
You might still get a fake from this, or any other marketplace or vendor. The way to check for this is to use a program called H2testw. If you can't use that program, you can also fill up the card with copied data and then check if the data is still valid. Personally, I'd throw it into a USB3.0 reader and load it with large videos, and then try watching the movies from the memory card.