There's a tool to find #mastodon handles of your #Twitter followers - and to bulk-follow them here on #Mastodon! Big thanks to @jwildeboer for pointing this out.
For all folks coming in via #twittermigration (#heuhier, #IchBinNeuHier):
==> fedifinder.glitch.me/ looks for your Twitter followers on Mastodon and let's you download a CSV which you can import on (Settings -> Import and Export -> Import on Mastodon web).
Find Fediverse accounts of your Twitter followings
Extract the fediverse handles and urls of your Twitter followings.fedifinder.glitch.me