Vibed up some quick code to get this... I'm mainly probing the instances of random people that I follow, and *some* of them federate with Nostr:
Instances federating with 'mostr.pub' or 'momostr.pink': - mastodon.world
fosstodon.org
retro-gaiden.com
doesstuff.social
sfba.social
defcon.social
dice.camp
mastodon.sdf.org
But many of the big ones, like Mastodon.social, don't...
nostr:nevent1qvzqqqqqqypzptujz495l5qzjfqrzwr0wyenkzhajaq6qah4cuutcfsr5k6e6eclqy0hwumn8ghj7mn0wd68yttjv4kxz7fwv3jhyettwfhhxuewd4jj7qgswaehxw309ahx7um5wghx6mmd9uq3kamnwvaz7tm5wfjkuerfdenjuun9d3shjuewd3skuep0qqsxnyp6wkks2eucuylljup88nq4qs8vujtp5aumc4dczcwwqxfuqhg602g66