Find private key filename for X509Certificate2 (inc CNG)

using Security.Cryptography.X509Certificates; //uses CLR Security from https://clrsecurity.codeplex.com

//certificate is a standard  System.Security.Cryptography.X509Certificates.X509Certificate2

if (certificate.HasCngKey())
{
    System.Security.Cryptography.CngKey privateKey = certificate.GetCngPrivateKey();
    bool privateKeyIsExportable = privateKey.ExportPolicy == CngExportPolicies.AllowExport;
    string privateKeyFileName = FindPrivateKeyPath(privateKey.UniqueName);
}

    private static string FindPrivateKeyPath(string keyFileName)
        {

            IList<string> searchDirectories = new List<string>(new string[] { @"\Microsoft\Crypto\Keys", @"\Microsoft\Crypto\RSA\MachineKeys" });

            string keyDirectory = null;
            foreach (string searchDirectory in searchDirectories)
            {
                string machineKeyDir = string.Concat(Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData), searchDirectory);
                // If found
                if (Directory.GetFiles(machineKeyDir, keyFileName).Length > 0)
                {
                    keyDirectory = machineKeyDir;
                    break;
                }
            }

            // Look up All User profile from environment variable
            if (string.IsNullOrEmpty(keyDirectory))
            {
                // Next try current user profile
                string userKeyDir = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) + @"\Microsoft\Crypto\RSA\";

                // for each sub keyDirectory
                foreach (string subDir in Directory.GetDirectories(userKeyDir))
                {
                    // Seach the key file
                    string[] fs = Directory.GetFiles(subDir, keyFileName);
                    if (fs.Length == 0)
                    {
                        continue;
                    }
                    else
                    {
                        // found
                        keyDirectory = subDir;
                        break;
                    }
                }
            }

            if (string.IsNullOrEmpty(keyDirectory))
            {
                return "Private key exists but is not accessible";
            }

            StringBuilder sb = new StringBuilder();
            sb.Append(keyDirectory);
            sb.Append(Path.DirectorySeparatorChar);
            sb.Append(keyFileName);
            return sb.ToString();

        }