Get the car on a lift and turn the wheels all the way. Find out what is stopping them from going further.
If something is hitting something else, see if you can cut/trim or even remove that piece. Of course dont go cutting important things such as control arms etc..
If nothing is touching anything else visibly, then remove the inner tie rod boots on the steering rack and see what is stopping the rack from moving more.
On a lot of racks, the rack itself can go further, but the part of the inner tie rod that bolts to it, hits the rack housing. To fix this you need to make spacers, or have the inner machined so it can slide into the rack tube just like the rack bar itself slides inside.
If the inner tie rod is not contacting anything on the rack, then chances are that the rack simply can't go further because it doesnt have any more teeth cut into it
to fix this you can:
1-have more teeth machined into it
2-change to a different steering rack (not easy)
3-modify the spindles, so that the outer tie-rod mounts closer to the steering axis.
With option 3 your rack will still move the same, but for each mm of travel, it will pull the spindle more degrees because of the shorter lever arm. This will increase your steering ratio meaning less turns lock-to-lock, but increase steering effort also.
My BMW has this done to it and I can get some big angle now, if I want more I need to make longer control arms because my tires hit the inner frame. This is with only shortening the steering arm by 30%.
If you choose option 3, make sure you have a qualified fabrication shop do it, because the welds need to be good, and both sides need to be identical.
Oh and like everyone else said, just keep at it.
By the way I am the guy who you gave a ride across the street from Pizza Hut to the gas station at DriftFury Charlotte county.
Also I drifted a blue S2000 at the Hialeah Slide event back in 2004 and I liked the cars dynamics a lot. I never really noticed a lack of steering angle, the car is just very responsive so you have to be smooth and controlled with your inputs. It could also use a lysholm supercharger to give the damn thing some real bottom end.