Dark Elves of Myth? I'm not sure what mythology or group of Folk Tales you mean. In the various European Mythologies beings who can be equated with Tolkien's Elves (ie. man-like, man-sized, beautiful, immortal, poetic, magical, and skilled) are seldom evil, as the name "Dark Elf" would suggest. They could be fey, dangerous, even malicious but not evil as such.

Dark Elves as a kind of evil doppleganger of Elves seem to have been the invention of the original Dungeons and Dragons creators. The concept then being used by authors such as Feist who were particularly influenced by D&D in their "World-making" and plots.

As for Tolkien there are no evil Elves at all. Tolkien's elves were capable of performing evil acts under the pressure of circumstances (eg. Feanor's kin-slaying) but no Elves were inherently evil.

However if you consider orcs as a form of elf, as Morgoth warped some early elves he had captured into orcs, then they would be classifiable as "Dark Elves." I think this is just a formal point as I'm sure Tolkien did not consider them so.