You can buy ladybugs from a garden supply company and release them in your garden. Ladybugs are a beneficial insect. They are beneficial to your garden because they eat many of the insects that would do harm to your plants.
One place you can buy ladybugs is: http://gardeningzone.com/
In addition, Gurney's Seed & Nursery Company sells a 'Beneficial Bug Blend'. This is a package of seeds which, when planted, grow into plants that attract beneficial bugs.