Slotting in Welcoming Vampire to replace Sporemound is a good choice, reducing the overall casting cost curve of your deck a little and replacing a card that relies on landfall triggers to be good, something the deck isnt optimized for
5C mana-fixing rocks like Chromatic Lantern, Fellwar Stone, and Coalition Relic are perfect here, but even the signet cycle (Golgari Signet) and the talisman cycle (Talisman of Creativity) do a great job here
Thats almost ideal in decks that want to draw and discard a bunch or decks that play wheel effects
Oh and Vanquisher's Banner, Herald's Horn, all pretty deece tribal stuff
March of the Machine, for instance, has tons of serialized cards, but its Collector Booster boxes are only $400