Mudugards?
i've successfully fitted a full length mudguard to a 440mm pair of rigid forks by hammering a star nut into the bottom (lots of effor, the steerer is thicker at the bottom) then attaching a long bolt (bought from halfords) to the star nut, with a few nuts on it to hold the 'guard in place. i had to drill a hole in the'guard.
it works quite well, and looks very neat.
For the stays at the bottom of the fork you could use P-clips if they will fit round the fork legs.
I think old non-suspension rigid forks for MTb's were 400mm long ish, anything longer and its difficult to mount a full mudguard close enough to the tyre, hence the above bodge.