Yeah, this is a bit of a task as it's all eight badges of one reason. Feel free to say no as a lot of dedication and creativity would be needed to fulfil this task.
Badge Type: Normal
Badge concept art: Something bland would be preferable. Perhaps something in the shape of a dog bone?
Badge Type: Fighting
Badge concept art: Quite generic considering its type but something that fits in with 'fighting' would be appreciated. I would ask for a fist but that's used for Brawly's gym in R/S/E. How about a foot this time? n_n
Badge Type: Fire
Badge concept art: Really generic here; but hey, it's a Pokémon game it's hard to really do anything different in Pokémon etc. So pretty much some flames or lava will do here.
Badge Type: Electric
Badge concept art: Pretty much the same as above here. It's hard to differentiate with electric types so we're going to have to go with something like a thunder bolt or something.
Badge Type: Dark
Badge concept art: Hm... Not totally sure what to do here. How about some shadows? Some snake eyes, they seem kind of dark. I guess you could do whatever you want here.
Badge Type: Flying
Badge concept art: Just some wings or something would probably do here. Maybe some clouds, whatever looks best in your opinion really.
Badge Type: Rock
Badge concept art: Just a fancy rock or something I guess n_n.
Badge Type: Dragon
Badge concept art: I'm seriously struggling on ideas here. I definitely don't want anything animal shaped... Perhaps a star or something? I know it doesn't make sense but whatever.