Well, you can always upload your level.dat save file to something like MineAtlas where you can see your world and find any biome you wish (it's old, for 1.8, but it's fairly accurate, and you're looking for swamps, not underwater ruins).
If you prefer not to do that, note that swamps commonly border other similarly-temperate biomes like plains, forests, dark forests, beaches, and jungles. If you find any of these biomes, which are all fairly common (sans jungles), you may find a swamp nearby. They are fairly common.
Rollback Post to RevisionRollBack
LP series? Not my style! Video series? Closer, but not quite. Survival journal, maybe? That's better. Now in Season 3 of the Legends of Quintropolis Journal (<< click to view)!! World download and more can be found there.
If you're open to using Mods try Scenter-1.12.2-3.12.0.jar. When you use something in your tool-bar, a colored large X displays the direction to clay once configured, if there is any clay in the vicinity. You can also configure the color of that X and an outline of the clay in this case.
I don't believe it has progressed beyond 12.2, and I think it needs Forge.
Need more help PM me, please.
It does work, I tried just it.
Scenter can be configured to find many things, but only one at a time.