The serial number doesn't help us. We need to know your model number.
Roku only offers a replacement cable with the WiFi receiver for one model, the 3820/3821 ( I know that's two model numbers, but it's the same basic device). However, even that one is shown as Out of Stock on the Roku products page. It's been out of stock for some time, so I have no idea when it might be available again.
If you have a 3820/2821, you could wait until Roku gets it back in stock. If you have any other model, or don't want to wait on Roku, then perhaps you can find one on eBay or other online site. Just make certain the product offered will work on the model you have.
Dan
Roku Community Streaming Expert
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