Keyword searching is the most common strategy for finding secondary sources. However, you should not rely on keyword searches alone. There are number of other strategies that you can utilize to cast a wider research net. Incorporating the additional research strategies listed below may help you find sources that traditional keyword searching missed.
You can use Google's site/domain level search feature to find reliable data and other resources freely available on the web
Where you look for data depends on the type of data you need.
There are two types of data:
Free/Open Access e.g., government, NGO, and non-profit organizations data
Paid access (behind paywalls) e.g., commercial data