Martha Stewart [or any other reasonably good] brand of microglitter or FolkArt's extreme glitter - you'll get them in craft/hobby shops, usually with card making or scrap booking. You should make sure to include silver in whatever colour you are doing as most MLP glitters have a silver base. So do an underlayer of silver glitter and then an over layer of the applicable colour. And also remember MLP symbols were never overly generous in glitter content - do dont add too much!
Good luck.