If you can't find any information on breeding Swamp Snakes, you could try to set up a cage to mimic their natural conditions. Give a vegetated body of water with muddy, moss-covered bank on one side of the cage. Might take a 40 gallon or bigger but when I can't figure something out for situations like this online, I try my hardest to recreate it with what I know about the locality and natural habitat of the species.