Dusk // Dawn is tailor-made for this deck since you wont lose any creatures (aside from your commander), and ditto for Slaughter the Strong
They track the most popular and competitive decks in every format, and you can just buy a deck entirely through their site
Clan Defiance It may not look sexy, but Clan Defiance is the best X damage spell in Gruul, and better than most Red options with its ability to shoot down two creatures as well as Blaze an opponent
According to ComicBook, Ravensburger will release four new sets per year
Bouncing a damaged Kronk or The Prince, Never Gives Up can be a great way to heal them so they can be played again, while bouncing a shifted Hercules or Cinderella will always give you two cards back, and even allow you to add one of them to your inkwell if you're in a position to play the Floodborn card for full price
Not only will these get you back your instants and sorceries to make the deck go nuts, you can also get back permanents as well