Call Comcast to request a replacement or new receiver. The nationwide toll-free number to call is (800) 266-2278. Over the phone, a customer service representative can help you to complete most of the process to get a Comcast receiver. The representative can troubleshoot any problems, put in a request for a service technician visit (including drop-off of a receiver) or place an order to send a replacement or new box in the mail. In addition, the agent can put in your request to your local service center for pick-up if the local center has the receiver type/model that you're requesting in stock.
Contact your outside Comcast direct sales representative, if you have one, to request a receiver or for guidance based on your specific situation. Depending on your geographic location and the services offered, your outside sales representative may have the ability to personally come to your home and discuss any changes you want or need to make to your service package. At the very least, the representative can provide you with the best instructions for getting a receiver in your local area.
Visit your local service center to get an additional receiver. Most local service centers provide new product options. As long as new service activation at your home isn't required, you can typically pick up a receiver and take it home for use the same day if the type/model is available.