Which cable? The RF cable with F type connectors between the hub (and TV box) and incoming wall socket - probably via a splitter?
Or are you talking about an Ethernet cable?
F type cables, 1 or 2 metres long, are available from sites like eBay or Amazon for a couple of quid and also in pound shops. That said I understood VM want their own cables to be used to ensure signal quality - Virgin provided mine along with an Ethernet cable for the V6 TV box.
Example F Type cable here
But get onto Virgin to get replacement to their specification....
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I know a bit about Wi-Fi, Telecoms, and TV as I used to do it for a living but I'm not perfect so don't beat me up... If you make things you make mistakes!