Do you have official script copybooks from Yan Zhenqing or Ou Yangxun?

No, but there are strokes of official script and seal script in Yan style characters. Learning Yan-style regular script is of great help to learning official script. Lishu is divided into Fang Bi and Bi Yuan, with Fang Bi as the representative and Cao Quanbei as the representative. If you are a beginner, I suggest you study Two English Monuments, which is more neat and easy to use. After the foundation of official script, you can learn from Cao Quanbei, Shi Chenbei and so on.