Edit: C57BL/6NJ is a different strain (https://www.jax.org/strain/005304). But I am looking for C57BL/6J a.k.a B6 (https://www.jax.org/strain/000664). B6 is not included in the dataset you have shared.
Original: Thanks. Yes, it's indeed included - https://www.ebi.ac.uk/ena/browser/view/SAMEA1094237
Check https://www.mousegenomes.org/. It should contain the VCF files.
Thank you. I have already checked the page, but unfortunately, they do not currently have the VCF file available for the B6. They do have it available for other prominent strains.