I'm not sure if you're still looking for this information but this appears to be an incredibly convoluted yet working method of obtaining one (I say "appears to be" because I haven't tested it myself but it sounds plausible):
- Teach a Pokemon the HM Move Defog in D/P/Pt
- Trade the Pokemon to HeartGold or SoulSilver, where Defog isn't an HM move
- Transfer the Pokemon to B/W/B2/W2
- And finally, transfer the Pokemon to X or Y via the PokeTransfer/Pokemon Bank
Fun times.
Basically, the reason that Serebii was no help is because there's currently no way to actually get Defog onto Scyther without breeding it with something that learned the move prior to Gen VI. Hopefully that'll change at some point in the future. xp