This is easy but the final effect will not be vector but raster. Using AI 8.0, create your gradient using the gradient tool. Then rasterize the gradient by selecting it then choosing Object/rasterize... You will probably want to choose 300ppi from the dialog box. You won't notice much difference once that's done but this next step will create the effect you are looking for. With the gradient still selected, choose Filter/Pixelate/Color Halftone... from the pull down menu. Set the Max. Radius to a large number for large halftone dots. The effect doesn't exactly mimic real halftone dots but it's generaly good enough to achieve the look you describe.