Here the list of screws found on the Arrma Kraton:
AR721308 - BUTTON HEAD HEX MACHINE SCREW M3x8mm
AR721312 - BUTTON HEAD HEX MACHINE SCREW M3x12mm
AR721316 - BUTTON HEAD SCREW M3x16mm
AR721320 - BUTTON HEAD HEX MACHINE SCREW M3x20mm
AR721322 - BUTTON HEAD SCREW M3x22mm
AR721326 - BUTTON HEAD SCREW M3x26mm
AR721412 - BUTTON HEAD SCREW M4x12mm
AR721435 - BUTTON HEAD SCREW M4x35mm
AR721440 - BUTTON HEAD SCREW M4x40mm
AR722208 - FLAT HEAD HEX MACHINE SCREW M2x8mm
AR722305 - FLAT HEAD HEX MACHINE SCREW M3x5mm
AR722308 - FLAT HEAD HEX MACHINE SCREW M3x8mm
AR722312 - FLAT HEAD HEX MACHINE SCREW M3x12mm
AR722316 - FLAT HEAD SCREW M3x16mm
AR722320 - FLAT HEAD SCREW M3x20mm
AR722412 - FLAT HEAD SCREW M4x12mm
AR723312 - CAP HEAD SCREW M3x12mm
AR723328 - CAP HEAD SCREW M3x28mm
AR723410 - CAP HEAD SCREW M4x10mm
AR724303 - SET SCREW M3x3mm
AR724305 - SET SCREW M3x5mm
AR724310 - SET SCREW M3x10mm
AR724403 - SET SCREW M4x3mm
AR724410 - SET SCREW M4x10mm
AR724505 - SET SCREW M5x5mm
You might want to check out
www.mcmaster.com for screws as well. Usually find much strong screws, in bulk, and great prices.