Question

Where can I get the sprites like the extra ones Gary Oak had in the anime?

Answer 1

If you're talking about the gym badges that Gary has that don't appear in the games, then there is no way to get them. There isn't a gym for them, and they were only in the anime.
If you want to know why he has these mysterious badges, then this or this
are questions that answer it.

Other than that, we don't know what these badges are, but we can't get them in the game, since they don't exist.

Answer 2

I think you're talking about Gary's weird gym badges (I looked at the edit). There is no possible way to get their sprite since they do not appear in the games. We don't know what gym they were for and they only appear in the anime. You might be able to find fan-made sprites though.
Hope I helped!