I don't think there's a way to directly download the source from Vercel or v0. The best way though would be to deploy to Vercel and then connect to a git repo. From there you can either clone the repo locally or download as a zip directly from GitHub.

I used the "Add to codebase" approach outlined here:

https://www.reddit.com/r/nextjs/comments/1fzs4ji/comment/lz95cal/

Thanks for sharing this, @aruns!

This is the way I've done it in the past