Title explains it all, I tend to get at least 1 from a harpie or dagganoth task, but are there better monsters to farm for them?

Cockatrices(Relleka Slayer dungeon, 3rd room).Remember a mirror shield(else you will get hit hard and might even die). If you have access to slayer rings you might want to take a bob(terrorbird or better) and bank the eggs. Heard they sell for quite a bit in ge.