Your search for "plains 504" revealed the following:
Plains - Commander Deck (504) (CMR) from Commander Legends, available at 401 Games Canada. Rarity: Common Finish: Normal Artist: Noah Bradley
Sunbillow Verge (First-Place Foil) (DFT) from Aetherdrift, available at 401 Games Canada. Rarity: Rare Finish: Foil Artist: Pete Venters Card Text:T: Add W.T: Add R. Activate only if you control a Mountain or a Plains.
Plains (004) (PALP) from Asia Pacific Land Program, available at 401 Games Canada. Rarity: Common Finish: Normal Artist: Ron Spears Card Text:T: Add W to your mana pool.