Unfortunately, I am unable to browse the internet and provide specific information on where to find previous years' papers of UPSC Law Optional subject with the marking scheme mentioned for each question paper. However, I can guide you on how to search for these resources effectively.

1. Official UPSC Website:
- Visit the official website of the Union Public Service Commission (UPSC) at https://www.upsc.gov.in/.
- Look for the "Examinations" tab on the homepage and click on it.
- Under the "Previous Question Papers" section, you may find question papers of previous years for various UPSC examinations, including the Law Optional subject.
- Download the question papers and check if the marking scheme is provided.

2. UPSC Exam Preparation Websites:
- There are several websites dedicated to UPSC exam preparation that provide previous years' question papers and solutions.
- One such popular website is EduRev (

https://www.edurev.in/). https://www.edurev.in/).

- On the EduRev website, you can search for UPSC Law Optional question papers for previous years.
- Check if they have the marking scheme mentioned for each question paper.

3. Online Forums and Communities:
- Join online forums and communities where UPSC aspirants discuss and share study materials.
- Websites like Quora and Reddit have dedicated sections for UPSC preparation.
- Post a query asking for UPSC Law Optional question papers with the marking scheme mentioned.
- Fellow aspirants or experienced candidates may provide you with the required resources or guide you to the right sources.

Remember to be cautious while downloading resources from the internet and ensure that they are from reliable sources. It is always beneficial to refer to official websites and trusted platforms for accurate and updated information.