We will need around 300-400pcs per year.The first ½ inch under the head can be plain if it helps.
It does not need to be button head torx if it is difficult to get it, but as similar as possible.
We do not have any special description for the color, but we need a screw with as much as similar color as below. 
It needs to be corrosion resistant. 
Strength of material 10.9.
IMDS reporting and ISO 9001 are needed.