Hi Stan,
Yes the skinny mk.3 cables are still available, but they may not always be the best solution.... Personally, I no longer stock the thinner (2.5mm diameter) mk.3 cables, as the conductors inside are too thin for good sound quality and reliability in my opinion. Obviously, if the priority is being able to hide the wiring, then your B&O dealer will be able to obtain the thin cables and they should be able to find a part number for you.
However, if cable size is not critical from an aesthetic point of view, substantial gains can be made sonically by going for a 4.5mm diameter cable with OFC conductors and stronger construction. 
Kind regards,
Steve.
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