I recommend checking out Netprospex from Dun & Bradstreet. It is was I use and I found it to be reliable. You should know it is expensive. Data.com from Salesforce is Ok too. If it's in your budget, check out what kind of information they have and see if it meets your needs. If you can't find a service that collects the information you need, then you have to collect it on your own. This will be more expensive and time consuming. You will have to create a network of sites that host content that your potential audience would be willing to trade their information for.