Use natures compass to find a forest biome. Once there look for a surface cave, you should find plenty. If your still having issues, you can craft it with nether quartz and cobble (makes diorite), and diorite and cobble makes andesite. Or look underground for Occultism groves. The divination rod from occultism can also help locate some.
Diorite will spawn in Savanna, Jungle, and Mushroom biomes.
Granite will spawn in Mountain and Hill biomes.