You just have to breed them. Put flowers of the same type together and keep them watered, and you'll have a chance each day of finding hybrids. There are lots of guides online that show which colors make which hybrids. It's just a matter of patience.
I accidentally got hybrids at first. All I did was place flowers of the same type in patches together and watered them. It's fairly easy. For the harder hybrids, try arranging them in patches diagonal-ish and watering them. You'll need to put certain colors, in example two red roses, together to get certain hybrids.