I'm in the early phases of making the game, so I won't need the sprites for a while, but I'm making a Pokemon/Metroid crossover in Pokemon Essentials and I need DS Pokemon-style sprites for several Metroid creatures. The ones I know will be in the game are Parasite, Plated Parasite, Ice Parasite, Parasite Queen, Shriekbat, Metroid (all stages from Metroid II), Tallon Metroid, Hunter Metroid, Metroid Prime (both forms), and Ridley. I imagine there will be more when I get to it, but I'm focusing on the early game (besides Metroid Prime, which I know will be a final boss).
Also during the course of the game you will encounter several Phazon-infected Pokemon, which function very similarly to Shadow Pokemon except for how it's cured. Phazon Pokemon should have similar sprites to Shadow Pokemon, but more blue. The only Shadow Pokemon I've entirely decided on are the Gen 6 starters, for at least the first two stages of evolution.
I doubt any of these resources already exist, but I might as well get it out there.