You can convert any numeric integer primitive to its binary representation as a string with Convert.ToString. Doing this for everyone bytein your array and concatenating the results is very easy with LINQ:
var input = new byte[] { 254 };
var result = string.Concat(input.Select(b => Convert.ToString(b, 2)));
Update:
, 8 , , , . 8 , :
var result = string.Concat(input.Select(b => Convert.ToString(b, 2).PadLeft(8, '0')));