Not strictly for origami but Awagami has a really nice mixed bag of different types of washi paper of different sizes at a pretty good price.
I have seen it in Australia so you should be able to get it in the US. Note that most of the paper are not square, and you’ll need to find your own cutter and bonefolder. Alternatively look at https://www.origamishop.us/ and see what they have. The French equivalent has various sample packs that you can get, so there might be some in the US shop as well.
