widest possible front fork

g.fried said:

I have bought some motors having 120mm axle length - and desperately
searching some fork which fits...

Try China.

Yours is a common compatibility problem between Chinese-market hub
motors and US-market bikes, which almost without exception have 100mm
spacing on the forks.

The cheap and simple way to cope is to bend a normal bike fork to a
wider spacing. If the fork is of the "unicrown" type with vertically
parallel blades, you probably won't have a clearance problem between
the fork legs and motor housing.

Otherwise, you could have a custom framebuilder make something for
you, which cost at least $300 the last time I looked into it. One
major advantage to a fully custom approach is that you can have the
framebuilder provide thick, sturdy plate fork tips that won't be pried
open by motor torque at the axle.

The Surly Pugsley fork (not cheap) has 135mm spacing, but it's off
center, with the extra 35mm all on one side. Trying to make do with
one of those would mean having to offset the rim of your front wheel
by 17mm, which would make the wheel much weaker and less reliable.

Chalo