"Any way to warn other buyers about this seller?"
No. Unfortunately, you let time goes by. It is too late for feedback.
"What are my recourses?"
If you paid with a credit card through PayPal, you may be able to file a chargeback with your credit card issuer (bank). Call the toll free number on your monthly statement.
If you did not pay with a credit card, sorry, it is too late for recourse.