Most, if not all, metal building manufacturers make Z sections, so look on the website of one that has a plant close to you. Because cold-formed steel design can be so finicky, it is difficult to publish load tables because of all of the quantifying criteria that would have to be added. Is the z-section unbraced? How far? Is it supporting a through-fastened panel? Is it supporting a standing seam panel? I would suggest getting the CFS software. You can download a free version from rsgsoftware.com that will give you the capability to calculate section properties. The full version will let you design the purlin.