GetCertificate.cs

using System.Security.Cryptography.X509Certificates;

// GetCertificate
// Gets a certificate from the user's certificate store that matches
// the specified serial number
static X509Certificate2 GetCertificate(string serialNumber)
{
    using (var certStore = new X509Store(StoreName.My, StoreLocation.CurrentUser))
    {
        certStore.Open(OpenFlags.ReadOnly);

        var certCollection = certStore.Certificates
            .Find(X509FindType.FindBySerialNumber, serialNumber, true);

        X509Certificate2 certificate = null;

        if (certCollection.Count > 0)
        {
            certificate = certCollection[0];

            Console.WriteLine("Found a matching certificate");
        }
        else
        {
            Console.WriteLine("No matching certificate found");
        }

        return certificate;
    }
}