Sableye is your best bet. It's main attack lets you get two item cards from your discard pile. Almost all Darkrai decks run with it. It works because most D-rai decks run Dark Patch, which allows you to attach a Dark energy from your discard pile to one of your Dark Pokémon. You can also run this with Crushing Hammer and Enhanced Hammer, which discard the opponent's energy. Or there is Hypnotoxic Laser, which poisons and gives a 50% chance of sleep for the defending Pokémon. I run both hammers and lasers... which no one has replied to yet .-. so, just experiment with what works well with your style of playing.
As for electric types, Emolga would probably be your only option. Most other electric types require that you run Eelektrik to work well, and that would mean more electric energy. DONT DO THAT. Just stick with emolga
Have you thought about Mewtwo or Bouffalant for the deck? They're both great side attackers/techs.