My advice would be to get a brand new one from one of the authorised Ross-Tech distributors in the UK (bottom of
this page).
If you end up buying a genuine second-hand interface cable off
eBay then be aware that Ross-Tech charge $99 to transfer the support of a pre-owned cable to another user (see
this page) so take this into account when deciding how much to pay, bearing in mind that a brand new HEX-V2 cable costs £225 from a UK distributor including full support from Ross-Tech. Based on some of the prices I have seen second-hand genuine cables advertised for on
eBay it may work out cheaper to just buy a brand new cable if you want support for it which is invaluable when you own a complex piece of kit like this.