After sending a condolences card to a friend on the occasion of the death of his father, I realized I had a surplus of birthday greeting cards and no sympathy and few "Get Well Soon" cards. So I Googled "buy sympathy cards online muslim," skipped Hallmark and found myself in Etsy. After figuring that out, I have produced two public lists, one for Sympathy cards and the other for Get Well Soon cards which met my Muslim aesthetics. There is some overlap between the two lists.
I've also ordered from As the Heart Heals.
So, as I receive them, in sha Allah I'll update this to confirm that the vendors were legit. Also, the Etsy vendors were mostly from Canada and the United Kingdom. Do USA vendors use another platform?