Fenders
From Onewheel.Wiki
Jon Rambo Carbon Fiber
Comes in black and sometimes other colors. Supports screw-in and magnetic attachment.
Email him at njcustom908 AT gmail DOT com
Velcro fasteners
Scotch Reclosable Fasteners, Clear, 1 x 3-Inches, 2 Sets. I use this with the Future Motion fender instead of screws. It makes it easier to take off if I need to clear out wet leaves. Also during a crash, the fender will pop off instead of crack. The only downside is it creates a small gap between the footpads and fender that allows a tiny of stream of water through.
I tried "lower profile" Velcro but it doesn't stick well enough.