Here's at least one that ought do do nicely:

/// <summary>
/// converts a short into two component bytes.
/// </summary>
/// <param name="input">the short to break down.</param>
/// <param name="high">the high byte output of the function.</param>
/// <param name="low">the low byte output of the function.</param>
public static void FromShort(short input, out byte high, out byte low)
{
    high = (byte)(input >> 8);
    low = (byte)(input - ((input >> 8) << 8));
}

/// <summary>
/// converts 2 component bytes into a short.
/// </summary>
/// <param name="high">the high byte of a short.</param>
/// <param name="low">the low byte of a short.</param>
/// <returns>the short that the two bytes represented.</returns>
public static short ToShort(byte high, byte low)
{
    return (short)((short)low + ((short)high << 8));
}