you might get lucky check with Paul at just Engines on your side of the pond a PAW compression screw MAY fit if not find a socket head
screw of the same thread REGARDLESS OF WHICH WORKS MAKE SURE YOU DO NOT TURN IN TOO FAR THAT THE CONTRA PISTON
STRIKES THE HEAD you can check this by cranking down the screw and turn the engine gently by hand as you turn it in when and if you get contact back it off and make sure you do not go that low again
If you go the socket screw bit round the end of the screw si it is not a sharp contact