Are there .NET implementation of TLS 1.2?

Yes, though you have to turn on TLS 1.2 manually at System.Net.ServicePointManager.SecurityProtocol

System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls; // comparable to modern browsers
var response = WebRequest.Create("https://www.howsmyssl.com/").GetResponse();
var body = new StreamReader(response.GetResponseStream()).ReadToEnd();

Your client is using TLS 1.2, the most modern version of the encryption protocol

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Out the box, WebRequest will use TLS 1.0 or SSL 3.

Your client is using TLS 1.0, which is very old, possibly susceptible to the BEAST attack, and doesn't have the best cipher suites available on it. Additions like AES-GCM, and SHA256 to replace MD5-SHA-1 are unavailable to a TLS 1.0 client as well as many more modern cipher suites.

Just found that .Net Framework 4.5 now supports TLSv1.2
http://msdn.microsoft.com/en-us/library/system.security.authentication.sslprotocols(v=vs.110).aspx