Tools to Boost Email Scraping Success Beyond Apollo.io

Hey everyone, I’m using Apollo.io to scrape emails. I have company domain names as input and I’m looking for emails for specific personas (CEO/Founder, CFO / Finance Director / Finance VP). I’m able to retrieve only about 50% of the emails through Apollo. I'm looking for contact info. of people based in India. What other tools can I use to get at least 90% coverage?