using static System.Console;

using System.IO;

using System.Collections.Generic;

public class Program {

    public static void Main() {

        foreach (var file in FileUtil.GetFiles("c:\\", "aria2c.exe")) WriteLine(file);

    }

}

​

public static class FileUtil {

    public static IEnumerable<string> GetFiles(string root, string searchPattern) {

        var pending = new Stack<string>();

        pending.Push(root);

        while (pending.Count != 0) {

            var path = pending.Pop();

            string[] next = null;

            try {

                next = Directory.GetFiles(path, searchPattern);                    

            }

            catch { } //aqui você pode colocar log, aviso ou fazer algo útil se tiver problemas

            if (next != null && next.Length != 0) foreach (var file in next) yield return file;

            try {

                next = Directory.GetDirectories(path);

                foreach (var subdir in next) pending.Push(subdir);

            }

            catch { } //aqui você pode colocar log, aviso ou fazer algo útil se tiver problemas

        }

    }

}