I am sorry to hear about your Pro-HD not working anymore. Unfortunately the 350 model Slingbox does not have the built in tuner like the Pro-HD model did. Even if you were to connect a converter to it you will not be able to have the same features. The 350 model is still none the less a great unit to have.
If you do want the feature of the tuner you could always purchase another Pro-HD from Amazon. They are a retailed vendor of ours. If you purchase it through them you could also get a 1 year technical support warranty with a provided proof of purchase. The link below will take you to their website.
You could also call in to Sling Media technical support & set up a payment arrangement to get a replacement. It will cost to do so but it's always another option that you do have. The number to call is 1-877-467-5464.
I hope this information gives you a little more understanding of what options you have. Feel free to reply with any additional questions or concerns!
The Sling Moderation team