Finding previous years papers of UPSC Law Optional subject with the difficulty level mentioned for each question can be a challenging task. However, there are certain sources and strategies that can help you in this endeavor.

1. Official UPSC Website:
- The official website of the Union Public Service Commission (UPSC) is a reliable source to find previous years' question papers.
- Visit the official website at www.upsc.gov.in.
- Look for the "Examinations" tab and click on it.
- Under the "Previous Question Papers" section, you can find the question papers of various exams conducted by UPSC.
- Look for the question papers of the Law Optional subject for the desired years.
- Unfortunately, the difficulty level of each question is not mentioned on the official website.

2. EduRev:
- EduRev is a reputable online learning platform that provides a wide range of study materials, including previous years' question papers.
- Visit the EduRev website at www.edurev.in.
- Search for UPSC Law Optional question papers on the platform.
- You can find question papers from previous years, which will help you in your preparation.
- However, the difficulty level of each question may not be explicitly mentioned.

3. Offline Coaching Institutes:
- Many offline coaching institutes that specialize in UPSC preparation may have question papers from previous years.
- Visit these coaching institutes in your locality and inquire about the availability of UPSC Law Optional question papers.
- They might have materials that include the difficulty level of each question.

4. Online Forums and Discussion Groups:
- Join online forums and discussion groups related to UPSC preparation.
- Engage with fellow aspirants and ask for their guidance in finding previous years' question papers for the Law Optional subject.
- Some members might have collected or compiled question papers with difficulty levels.

Remember, while finding previous years' question papers is beneficial for practice, it is equally important to focus on understanding the concepts and developing analytical skills. Merely solving question papers without understanding the underlying principles may not yield the desired results. Hence, it is advisable to supplement your preparation with comprehensive study materials and guidance from experienced mentors or teachers.