chances are another bolt head will not fit the recess in the breech and may sit too high in the bolt trough not allowing the bolt to close.
Magnum air has them…star type Allen head….good luck
The nice thing about the Air Magnum torx head is that they are a rounded head and go a long way to eliminate the pellet hanging up issue. Plus, I have never stripped the head on one yet.
Instead of changing screws, get a precision .050 driver. PM your address and I will send you a Wiha.