Hoop Arm Screws are designed to break instead of causing severe damage to the machine itself.
Obtaining Additional Screws:
One additional screw is provided in the Operator's Kit with each new machine.
The part can be found here in the Parts Manual.
Extracting Broken Screw:
If enough of the screw is exposed on the top or underside of the carriage, a pair of vice grips might work. Otherwise, you would need something like this: