They are special PT (Plastics Technology).
Get them from your Starboard dealer as the best source.
Not sure you can sucessfully "outsource" them.
What year model board are you trying to replace the screws
All Starboards fron 1999-2008 used 6m x 29 mm long PT screws.
Starting in 2009 the length has increased to 32 mm.
Hope this helps,