Найти папку, а в ней файлы

DriveInfo[] drives = DriveInfo.GetDrives();

using System.Collections.Generic;
using System.IO;
using System.Runtime.InteropServices;

string[] GetCSharpFiles()
{
    foreach (var driveInfo in DriveInfo.GetDrives().Where(di => di.DriveType == DriveType.Fixed))
    {
        var dirs = SafeEnumerateDirectories(driveInfo.Name, "CLEO", SearchOption.AllDirectories).ToArray();
        if (dirs.Length == 1)
        {
            return Directory.GetFiles(dirs[0], "*.cs");         
        }
    }
    return new string[0];
}

[DllImport("shlwapi.dll", CharSet=CharSet.Auto)]
static extern bool PathMatchSpec([In] string pszFile, [In] string pszSpec);
 
private static IEnumerable<string> SafeEnumerateDirectories(string path, string searchPattern = "*.*", SearchOption searchOption = SearchOption.TopDirectoryOnly)
{
    Stack<string> dirs = new Stack<string>();
    dirs.Push(path);
    do
    {
        string[] subDirs = null;
        try
        {
            string currentDirPath = dirs.Pop();
            subDirs = Directory.GetDirectories(currentDirPath);
        }
        catch (UnauthorizedAccessException) { continue; }
        catch (DirectoryNotFoundException) { continue; }
 
        foreach (string subDirPath in subDirs)
        {
            dirs.Push(subDirPath);
            if (PathMatchSpec(Path.GetFileName(subDirPath), searchPattern))
            {
                yield return subDirPath;
            }
        }
    } while (dirs.Count > 0 && searchOption == SearchOption.AllDirectories);
}

foreach(FileInfo file in directory.getFiles())
{
    if(file.Name.EndsWith(".cs"))
        this.listbox.Items.Add(file.Name);
}

foreach (string path in GetCSharpFiles())
{
    listbox.Items.Add(path);
}

foreach (string path in GetCSharpFiles())
{
    listBox3.Items.Add(path);
}

return Directory.GetFiles(dirs[0], "*.cs");

return Directory.GetFiles(dirs[0], "*.cs", SearchOption.AllDirectories);

string[] GetCSharpFiles()
{
    var csharpFiles = new List<string>();
    foreach (var driveInfo in DriveInfo.GetDrives().Where(di => di.DriveType == DriveType.Fixed))
    {
        var dirs = SafeEnumerateDirectories(driveInfo.Name, "CLEO", SearchOption.AllDirectories).ToArray();
        foreach (string dir in dirs)
        {
            csharpFiles.AddRange(Directory.GetFiles(dirs[0], "*.cs", SearchOption.AllDirectories));
        }
    }
    return csharpFiles.ToArray();
}