Hoop Arm Screws are designed to break instead of causing severe damage to the machine itself.
For information on Seized or Stripped screw extraction see Stripped Screws - Overview. The below information is in addition to the overview article, and is specific to this screw.
Obtaining Additional Screws:
One additional screw is provided in the Operator's Kit with each new machine.
Replacement screws are available through the ShopMelco.com site:
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:
You might also need to check for a Missing or Damaged Helicoil Insert.