You can mount full mudguards to the fork using 'P' clips/clamps. They wrap around the fork legs and have a hole into which the mudguard eyelet is attached.
Look for rubber backed ones so they don't scratch the fork. The eylet goes between the two silver sections and you use a nut and bolt to tie them together.
The top of the mudguard i.e. 12 o'clock position can be attached to the fork bridge using the bolt hole (if it has one) or cable tie.