It is always excellent at the Cooper's Cask, as you say! I've had some terrible pints at the Mitre though. Usually Old, etc., presumably because they don't sell enough.
Longman is certainly the best alternative I've found.
I've genuinely never come across such a thing. If you can point me in the direction of one I'd be grateful. The closest is London Pride but it has nothing like the depth of flavour.