The Nord-lok cam design has been proven to maintain clamp loads over time where vibration is present better than aerobic thread lockers or nuts and does not effect your elongation.
"...best bet would be to get a 1" stripper bolt of sufficient length and turn down the threads, cut off the head, cut a slot to drive it. A big screw driver will drive a 1/4" bolt.
If you absolutely have to have an internal hex drive you could have made by EDM"
This is not an off the shelf...
The 12-24 is available depending on head and drive design. If not if your volume is big enough and you just can't get away from the screw and need 304 s/s versus the 18-8, find a Cold Header and have them made. Someone mentioned fastenal, here is their link below...
