It's been over thirty days.
Long enough to wait for an item from China, never mind North America.
Let your seller know once again that the cards have not arrived and ask for a refund.
If he refuses or is otherwise uncooperative go to the Resolution Centre at the bottom of this page and open an Item Not Received dispute.
The first step is to contact the seller, but you've already done that. Go to step two and escalate to a Claim.
If the seller does not refund promptly, Paypal will and go after him for their money.
You will not be able to leave feedback.
If the cards turn up after you have been refunded, you can return the refund using PP's Send Money service.
Do NOT accept an offer of a replacement. It won't arrive either.