cURL library - where can I get?

https://github.com/philsturgeon/codeigniter-curl

As noted on the page, it is no longer maintained, but I'm not aware of any specific issues in CI3. Links to alternatives are also included on the page, though you'll probably have to write a little code to adapt them for use in your application.

Bonfire

Practical CodeIgniter 3
CodeIgniter Testing Guide