compatible Shimano 3 speed left shifter (model: ST-EF51-AL)? I have a Carrera Subway Limited edition 2014 with V brakes. The front gears don't shift any longer since I recently got caught in a lot of rain. I've been told by a cycle repair that I need to change the left shifter plus the front derailleur.

The original left 3 speed shifter, model is: Shimano ST-EF51-AL, isn't been sold any longer apparently and I cannot find it on the net.

Is there anyone that could suggest what left shifter could I buy instead that is compatible with this model?
That's just a mountain Shimano triple flat bar shifter with a V-brake lever.

You can buy any left hand shifter which is marked for triples from the Shimano mountain lines: Tourney, Alivio, Acera, Altus, Deore. You may need a separate brake lever, which has to be sold for V-brakes and flat bars (it will look like the existing brake lever). Microshift also makes compatible ones, as does SRAM under their Attack! line. You can also use a friction shifter (cheapest option, eg. Sunrace SLM10). 

As an example, you can use the Shimano Acera SL-M310 shifter combined with the Shimano Acera BL-M421 brake lever. 



Go to your local bike shop, and they should have a ton of these parts on hand.