Convert WIA to ZIP

It is unlikely that you can just simply convert Nintendo Wii ISO images to ZIP archive, which is what wia to zip conversion would be. However, there are tool available like the Wimms WDF Tool with which you can open WIA images and extract the contents. Should you want, you can compress the extracted data to a ZIP archive, but there is not much of point to do that.

Simply put, it is impossible to convert WIA to ZIP directly.
Thus, there is no so-called wia to zip converter or a free online .wia to .zip converter to be found.