As you might expect Vegan chocolate means no diary products, so no milk no butter etc. in very simple terms any way. So dark chocolate vegan Easter eggs it is. But not all dark chocolate Easter eggs are vegan.
More Easter eggs are labelled dairy free rather than vegan, so I guess this have more to do with them being made in factory that also produces chocolate that contains diary rather than them not being vegan?
The four companies that do label there chocolate specifically “vegan” are:
Montezuma’s, Hotel Chocolat, Booja Booja and Divine. All the vegan Easter eggs are listed below.

Giant vegan Easter egg, the largest vegan Easter egg this year. This thick and chunky chocolate Easter egg is made from cocoa from Costa Rica with a rich aroma and flavour.
From Montezuma’s Easter range.
£19.99, 600g.
Labelled: GM Free, Preservatives / Additive / Colouring Free, Vegetarian, Vegan and Gluten Free.

Luxury dark chocolate vegan Easter egg with a selection of dark chocolate truffles and pralines.
Available from the Engraved Cocoa Pod Easter Eggs section.
£12.00 , approximately 220g.
Labelled: Vegan / Dairy Free, Vegetarian, Alcohol Free and Gluten Free.

Dairy Free dark chocolate Thorntons Easter egg, made under strictly controlled conditions to prevent any cross contamination from nuts, dairy, egg and gluten.
From the Thorntons Luxury Easter Eggs range.
£6.50, 120g.
Labelled: Vegetarian, Dairy Free and Gluten Free.

Rich, dark chocolate 70% cocoa solids – 100g Fair Trade Divine Easter egg with 80g of delicious dark chocolate covered Brazil nuts.
Made by Divine, available from the Chocolate Gifts section at the Ethical Superstore.
£4.99, 180g.
Labelled: Fair Trade, Vegetarian, Vegan / Dairy Free and Gluten Free.

Booja Booja – Luxury Champagne Organic Truffle Egg, 12 luxury Champagne truffles in a keepsake ornamental egg. Organic truffles from Booja Booja.
Available from a selection of online shops, see post for more details.
£19.95 – £20.99, 150g.
Labelled: Organic, Vegan / Dairy Free and Gluten Free.

Booja Booja Organic Around Midnight Espresso Egg 35g, three large organic coffee flavoured truffles in a velvet-lined keepsake egg.
Available from the Ethical Superstore – Chocolate Gifts section.
£8.99, 35g.
Labelled: Organic, Vegan / Dairy Free and Gluten Free.

Handmade vegan orange and geranium mini dark chocolate Easter eggs.
From the Montezuma’s Easter Chocolate range.
£4.95, 160g.
Labelled: GM free, Preservatives / Additive / Colouring Free, Soya Free, Vegetarian, Vegan, Organic, Gluten Free.