Hi Matty,
Sorry to say I have no idea what size your screws are..However they are Probably either Otto Bicycle thread...Or what they maybe,or could be, is the Tread Size of Enfield..As there are a loads of SMLE's in NZ...Why not look at Spare Screws from Enfield Rifles..as they (BSA) started production of the Cadet and Cadet Major after WW2 ...They may have utilised what came to hand around the Factory after-all they were probably still making Enfield's...
Good Luck
Regard's
Inproved...Steve...