Reddit mentions of A Field Guide to the Little People

Fairy-Faith in Celtic Countries by Walter Evans-Wentz, who was a fascinating character in his own right.

Examines the beliefs in the Celtic regions of Wales, Ireland, Scotland, Isle of Man, Cornwall and Britanny in regards to the fey at the very beginning of the 20th c.

Here's the table of contents:http://www.sacred-texts.com/neu/celt/ffcc/

The book is widely available online: the amazon cite includes a free version on kindle, project gutenberg also has it online.

It's a classic.

If you want a compendium of little people, fairies, gnomes etc. A Field Guide to the Little People is wonderful.

Katharine Brigg's An Encyclopedia of Fairies: Hobgoblins, Brownies, Bogies, & Other Supernatural Creatures is another classic.

You must read at least one of R.J. Stewart's books on the subject of faery healing.

Bit of an out-of-the-box suggestion but perhaps pick up a copy of https://www.amazon.com/Field-Guide-Little-People/dp/0809044501 or something similar. The one I linked is full of descriptions of real world fey/faeries from European folklore, and each description usually includes some sort of short cautionary tale. You might be able to find online collections of such folklore if you search for stories about "the Little People" or "the Fair Folk."

Once you get a handle on how the stories tend to run (usually involving someone ignoring/following old superstitions and being punished/rewarded or making a deal with a fey and either keeping it or breaking it) it should become easier to come up with new ones on the fly, and gives you a much wider cast of oddball fey to pick from than usual DnD lore really gets into.

Hope this helps!

Here!