I wrote a nano tool that tries to extract the #Fediverse accounts of your #Twitter followings: https://fedifinder.glitch.me/
It searches for the patterns @user@host.tld, user@host.tld and host.tld/@user in the screen name, description, location and URL field. It displays them to you in the correct format for easy copying as well as a CSV download that can be imported to #Mastodon.
Known issue: Mail addresses are included as false positives because people write their handle without a leading @: name@host.tld
GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.