using System;
using System.Text.RegularExpressions;
public class Test
{
    public static void Main()
    {
        string str = @"<a href=""/find/1"">testing</a>
                        <strong>a known text</strong>
                        <p>testing2</p>
                        <p>this paragraphs are dynamically</p>
                        ...
                        <a href=""/find/2/"">testing again</a>
                        <a href=""/find/3/"">testing and again</a>";
        var regex = new Regex(@"(?:a known text|(?<!^)\G)[\w\W]+?((?<=<a\ href="")/find/.*?(?=""))");
        var result = regex.Matches(str);
        foreach (Match match in result)
        {
            string matched = match.Groups[1].Value;
            Console.WriteLine(matched);
        }
    }
}