Sometimes, you can find a Vegvisir Bonemass in ruined towers in the swamps, and you usually get some crypts in the Bonemass swamp.
If there's a good difference in height between the swamp strip and the bordering biome, you may have the luck to find a muddy scrap pile partially buried under the slope.
Last but not least, try to cross the ocean from your swamp strip, you usually get another swamp on the other side.