There are a couple of official sources. The ELC Website and the ELVC website. I thought it would be useful though to combine each of the map squares into a single document.
The earlier presentations from 2015 were based on the old premium topo. The recent ones now use the new OS standard (to my mind inferior for navigation purposes). Neither of them are especially clear on zooming in, which is a pity.
22 maps old style
22 maps new Style
For completeness the old and the new style are presented here, as previousy published (link direct to the original source).
Old version (ELCV)
New version (ELC)
Map A Gullane, Aberlady and surrounding area
Map B North Berwick and surrounding area
Map C Whitekirk and surrounding area
Map E Prestonpans, Port Seton, Tranent North
Map F Longniddry and Haddington West
Map G Haddington East and surrounding area
Map H East Linton, Stenton and surrounding area
Map J Dunbar and surrounding area
Map K lnnerwick and surrounding area
Map L Musselburgh south and Whitecraig
Map M Tranent south, Macmerry, Ormiston
Map N Pencaitland and East Saltoun
Map O Gifford and surrounding area
Map P Garvald and surrounding area
Map R Oldhamstocks and surrounding area
Map S Glenkinchie and South West area
Map T Humbie and surrounding area
Map U Western Lammermuir Hills