I would like to buy a 16mm Fish eye lenses?

I would ideally like a little zoom on it, I'm not sure on best lenses to fit my Nikon D5000. Where is the best place to get it online or shop wise and does anyone have recommendation for a lenses please.

Since your camera is a crop camera, you will probably want something in the 10mm range or less.

Unfortunately, Nikon's 10.5mm fisheye lens will not autofocus on your camera.

You may have to look at Sigma or Tamron for an acceptable fisheye.

You must bear in mind that almost all 16mm fisheye lenses are designed for cameras with a full frame sensor, as a result you won't get that distinctive fisheye effect on a D5000. You will need a DX format fisheye lens. Sigma's 10mm fisheye should do the job nicely.