well first it's good to know exactly what's restricting lock. the steering rack only moves so far, the knuckles have a stopper which corresponds with a little tab on the LCA which stops lock, the tyres can foul against the chassis rails, and the knuckles start binding past a certain amount of steering angle.
so first things first, u can put some steering rack spacers which allow the rack to move further. from here the knuckles will start to stop on the LCA's, so u will need to modify either the tab on the LCA, or the stopper on the knuckles. around the same time u will have issues with tyres fouling on the chassis rails depending on what tyres/wheels ur running. if the tyre is big enough and offset is high enough u will have issues. for example i scrub with 5mm rack spacers, 17x9 +24's with 235/45's. few things u can do to stop this, either go lower profile, thinner tyre, or lower offset. u can also go longer LCA's like R33 ones which push the wheel out a bit further.
from there u will start experiencing binding issues on the standard knuckles, so then the next step is new knuckles or cut and shut ones. this can change things like ackerman angle, length of the knuckle, shape etc etc, which not only provides more lock, it reduces binding and changes the feel in the steering, as well as the turn ratio.