This is very illuminating; I am the proud owner of a pair of Sharks, and thought I should be in the market for a couple more. But it seems that on the Eastern at least, they only hunted in pairs.
In my extrapolation of the universe, these would be notionally allocated to the DCE Edinburgh, so probably at Slateford. It occurs to me now though, that to have any more would be overkill, and bring in another DCE, Carlisle perhaps. They're not cheap from the Hornby aftermarket so this should trim my wants list by a few quid.