The original screws are M3x0.5, which are 3mm with a 0.5mm thread pitch, and are 8mm long (measured from the underside of the head). They are stainless steel (I assume 18-8) with a
Pozidriv pan head.
The screws in both of the MK2a sleds I looked at have damaged heads, which leads me to believe that a phillips driver was used to install them during manufacture instead of a Pozidriv driver.
McMaster-Carr has a similar screw with a #1 phillips head as item #
92000A118 for $4.66 for a package of 100.
I would also strongly recommend using a low strength (purple) thread locker such as MG Chemicals 8701, Permatex 24024, or Loctite #222.