Usually very small aperture lens are only available in prime lens, that is a lens that has a fixed focal range.  Like Canon makes a 50mm f1.8, and even a f1.4.  Several other companies makes ones that go lower.  But when it comes to zoom lens, you won't really find one with a low aperture.  Nature of the lens and physics.  
I have a cannon mirrorless and have a 22mm f2 lens and a 50mm f1.8 lens for when I need a low aperture, awesome blurry bokeh background type of shot, but all my zooms, 15-45 and 55-200 start at like f3.5 or 4 and go up from there.