Back in 2015, Twitter provided the feature to export and import lists of blocked users, unfortunately they discontinued this service.

In order to fill this void, https://blocktogether.org/ provides a great service to allow users to subscribe to public block-lists that are always kept updated by some maintainers, unfortunately they have capacity issues and needed to impose limits on number of subscribers and list length.

I have written a small Python script that can provide a self-service import and export functionality using the Twitter API.

See https://github.com/zonca/twitter_blocklist