Ah. I almost got 3, but I think I need 4:
Kingdom:
Scrap, Rogue, Mandarin, Paddock, Capitalism
Loop:
Setup: Trash down to a deck of Scrap, Rogue, Paddock x 2, Mandarin, Horse x 4, (from Scrap or Paddock). Empty two piles for Paddock.
Play Horse x 2, drawing rest of deck.
Play both Paddocks (gain 4 Horses, and enough actions for the Rogue later).
Play Scrap, trashing Mandarin for all benefits except Silver. (gain 1 Horse, draw 1 Horse)
Play Rogue, gaining Mandarin from trash. Paddock x2, Scrap, and Rogue go onto deck.
Play Horse x 3. Draw Paddock x 2, Scrap, Rogue, Horse x 2.
Edit: this might require more than 4 Horses, but since I tested it multiple times and never ended with *exactly* 4 Horses (always more), it shouldn't be a problem.