cc: @Jakub Rudnik might be relevant

Any reccs on how to go through 1k+ signups a day to identify people with big audiences?

Yes. Add it as part of your onboarding flow (assuming you're already asking for job title etc.), might be harder in a B2B context though OR Send out an email to your list asking who's influential and would like to promote for % - customers are the lowest hanging fruit when it comes to promoting. You could just give away annual free subscriptions to influencers and get posts (if they're already on free trial)