You can buy Mr. Li Fangming's running script. In addition, Mr. Tian Yingzhang and Mr. Ding Yongkang can also buy from Pang Zhonghua.
Of course, pen calligraphy is far less expressive and vital than brush calligraphy. If you want to travel in a broader and deeper artistic world, I suggest you learn brush calligraphy, which can also promote your understanding and application of hard pen calligraphy.
In addition, it is not enough to learn pen calligraphy, but also to write Copybook for calligraphy, a famous ancient writer. Because of the characteristics of the pen itself, not all ancient calligraphy posts are suitable for writing with a pen. Here, I recommend some suitable books for you, such as Preface to the Lanting Pavilion by Wang Xizhi, Gu Bimu's Post by Wang Xianzhi, Luo Shenfu by Zhao Mengfu, and the inscriptions of Wu Niu and so on. These famous posts have stood the test of history, and their artistic charm is far higher than Copybook for calligraphy published by modern people.
Finally, I wish you progress every day. O(∩_∩)o ... Haha.