There may be some confusion regarding the meaning of "fisheye".
A true fisheye lens creates a curved distortion (aka "curvilinear wide angle lens") for any "straight" line in the image (with the exception that if the line happens to pass through the center of the optical axis then that line would remain "straight").
E.g. if you photography a door or window... the sides of the door will curve rather than remain as straight lines.
The more common wide-angle type is "rectilinear" ... these lenses keep all straight lines as "straight" lines. Lines that are parallel in real life will not necessarily appear "parallel" in the image... but they *will* appear "straight".
Do you want curvilinear distortion (true "fisheye") or do you just want a very wide-angle (rectilinear) lens?
Canon does make a true fisheye... it's the EF 8-15mm f/4L Fisheye USM. I *think* that's actually the only fisheye currently in the lineup. That lens is also a zoom.
A quick search reveals (besides the Canon lens) there are choices from Sigma, Tokina, Rokinon, and a few others ... offer choices that are true fisheye lenses. Tokina might be the only other vendor (besides Canon) that I see offering a zoom fisheye.