Your search for "swamp 303" revealed the following:
Swamp (301) (FIN) from Final Fantasy, available at 401 Games Canada. Rarity: Common Finish: Normal Artist: Fang Xinyu
Swamp (273) (AFR) from Adventures in the Forgotten Realms, available at 401 Games Canada. Rarity: Common Finish: Normal Artist: Adam Paquette
Swamp (143) (ARC) from Archenemy, available at 401 Games Canada. Rarity: Common Finish: Normal Artist: Susan Van Camp
Swamp (300) (Foil) (FIN) from Final Fantasy, available at 401 Games Canada. Rarity: Common Finish: Foil Artist: Domenico Cava
Swamp (003) - Arena League Promo 2003 (PAL03) from Arena League 2003, available at 401 Games Canada. Rarity: Rare Finish: Normal Artist: Rob Alexander
Swamp (302) (Foil) (FIN) from Final Fantasy, available at 401 Games Canada. Rarity: Common Finish: Foil Artist: Sean Vo
Swamp (033) (Foil) (SLP) from Secret Lair Promo, available at 401 Games Canada. Rarity: Rare Finish: Foil Artist: John Avon
Swamp (033) (SLP) from Secret Lair Promo, available at 401 Games Canada. Rarity: Rare Finish: Normal Artist: John Avon
Swamp (290) (30A) from 30th Anniversary Edition, available at 401 Games Canada. Rarity: Common Finish: Normal Artist: Dan Frazier Card Text:This version of this card has a non-standard Magic back. It is not legal for constructed play.
Tainted Isle (DSC) from Duskmourn: House of Horror Commander, available at 401 Games Canada. Rarity: Uncommon Finish: Normal Artist: Alan Pollack Card Text:T: Add C.T: Add U or B. Activate only if you control a Swamp.