Rubber Trees are rare compared to the normal assortment of flora in Minecraft. They are, however, much easier to find within Swamp Biomes. Like all other trees, they are impossible to find in Desert Biomes. Rubber trees have dark colored wood, like Pine, with bright leaves similar to Birch, and have a unique 'wing' in the leaf pattern. It is easier to locate Rubber Trees from a high point as they are identifiable due to a column of three leaves on the top of the tree, this is very helpful when in a forest biome and there are many different trees.
Shears will not break the Rubber Tree leaf block instantly, but it will drop the leaf block after it's done breaking.