I know this is a long shot, but here goes..
A friend of mine has recently restarted Y, meaning he's lost all of his items. He's not so worried about the other megastones, but Blazikenite was an event item, so he won't be able to get it back. He is, however, willing to trade whatever. (If I have what you want for it, I'll trade it myself)
If anyone's got one, he's also looking for a shiny ponyta, although I think that would be pretty cool to have myself xD