I would like to research Fairies and their wonderful virtues, as described in Celtic mythology. Can someone suggest rich and readily available sources on the subject?
You can find a lot of sources on Internet Sacred Text Archive ...
You have to scroll down to approximately 7/8 and you can find all the fairy texts you need. Or ctrl-f fairies.
Katherine Mary Brigg's The Vanishing People: Fairy Lore and Legends, is a good source, as well as Evan-Wentz's The Fairy Faith in Celtic Countries and Robert Kirk's The Secret Commonwealth. They're all out of copyright, so at least some of them are in the Sacred Texts.
I'd also recommend Diane Purkiss' At the Bottom of the Garden as a more modern look at fairies, as well as Barbara Rieti's Strange Terrain, but they're hard to find. Both focus on the darker side of fairy lore such as straying and changelings, and why people would tell such frightening stories.