概要

var start = new DateTime( 2018, 1, 1 );

var list = Enumerable
    .Range( 0, 365 )
    .Select( c => start.AddDays( c ) )
    .Where( c => c.DayOfWeek != DayOfWeek.Saturday && c.DayOfWeek != DayOfWeek.Sunday )
    .ToArray()
;

foreach ( var n in list )
{
    Console.WriteLine( n );
}