I couldn't find a Canadian (or any foreign) retailer that would ship to the US, but I found tons of US retailers that allow self-entry (as an alternative to uploading a signed prescription) as I described.

ContactsExpress ships to the US. There is at least one other that escapes me.

1-800 contacts will write a prescription for you with a $20 online eye exam.

Optomitrist asks if your current prescription is ok, asks you to stand 20ft back and read a few letters and you’ve got a script you can use wherever.

As will several other retailers, but only in some states. As someone in an excluded state, I considered whether enabling Mock Location on my phone would get me past that check (I think they require you to use a native mobile app, so I assume they use location from that?) but then thought of the method I mentioned earlier instead.

Reading all that, I'm happy my part of Europe is a bit behind the tech curve here.

I mean holy fuck, "native mobile app" and "getting contacts" do not belong in the same sentence in any sane universe.

Haha well the thing is, a vision exam requires that you read letters of a certain height from a certain distance while proctored, and presumably this is quite difficult to achieve in telehealth with more open computer systems. Of course some folks can figure out how to break anything (I mean, just plug a projector/TV into your phone with a usb-hdmi adapter and now the letters are huge?) but I think it keeps things easy and reasonably accurate among normies.