A quick (and not comprehensive) search yields:

Torx with "security peg".
Torx Security Seatpost Binder Bolt | Bicycle Bolts
https://www.missionbicycle.com/store...security-bolts

Automic22 Seatpost Bolt
Seatpost Lock - Binder - from Atomic22

You could also run a 1/4" cable from the seat rails to the seat stays. Crimpers are available to make it look like it was meant to be there, then you would decide if you wish to lock it in place, or make it permanent.