Chris,
Opportunities is a database of websites from the Internet, there is no one source.
This is up to your strategy to determine why they would need your services. It depends what services you provide.
As an example: I myself provide Magento services to Fashion clients – I have a good portfolio with those kind of ecommerce sites. I know that Shopify is not offering all the things that Fashion industry needs, so I show to those sites’ owners why using Magento is a better solution.
An another example are low quality restaurant websites created by Godaddy Website Builder. If you check some of those sites, they are look horrible, and they are own very often by fancy restaurants which can afford a better website. This is a great target!
What is your target market?