1. You need something called a technographic product to get lists of companies that use a particular technology. Though these products are notorious for having stale data, so make sure you do some cross-checks to ensure it's somewhat accurate (IE. lookup their IPs and see if they're really hosted on AWS). I haven't used Builtwith in awhile, but they're the leader in that category. Bloomberry is another one.

See Builtwith: https://trends.builtwith.com/websitelist/Amazon and Bloomberry: http://bloomberry.com/data/aws/

2. As someone else mentioned in this thread: job postings can be useful. You particularly want to look at job postings that mention AWS AND FinOps. FinOps = basically engineering to save costs for cloud costs. That is a very high signal they're investing in someone who can help them save costs (albeit a lot of job postings these days are fake, so it's not a 100% sure signal)

3. Combine the first 2 methods with headcount data from Linkedin or Cloudflare radar traffic data to find companies that are using AWS and growing the fastest, or having huge traffic spikes. Those are probably highly correlated with the desire to want to reduce AWS costs.