Speedfight 2 front brake caliper

Hi all my son has an issue with a rounded off bleed valve on his front caliper. It won't budge even with the mole grips so I though about drilling it out and using a bolt/stud extractor.
What I need to know is what size bleed valve does the caliper take and are they available to buy,
Second if this fails to work and I'm unable to source a replacement does any other caliper off a similar scooter fit.
Any info would be great.
Thanks in advance
Kev