The trick is there's almost always a findable signal even with no official list. Highest to lowest: the linkedin event page attending tab plus anyone posting with the hashtag, then sponsor and speaker lists since those companies always send people, then everyone engaging with the host's pre-event posts. Last year's sponsor list usually repeats too.
Full disclosure, I'm at Bitscale. The "who's posting about the event" part we actually walked through end to end in a session last week, pull everyone talking about the conference, enrich, filter to icp, schedule it to catch new ones as they post. Happy to share the link or talk through setup for whatever event you're targeting.