Best way to find references for statements in the thesis I am struggling finding proper references for the known facts that are mentioned in my thesis.

For example: foundation of Cartesian coordinate system introduced the grid system for data visualization techniques.

How can I possibly find a reference to support that claim?

What is your best method for finding references?
Although the question is a bit vague, I try to give you an answer from my experience. There are often statements that you heard somewhere or which are "obviously" true, but you need a reference. 

My best bet is to search google scholar for a variety of different combinations of the terms or suspected authors. If you find some source stating the claim (or something similar) you can often go back through the chain of citations to find a more accurate and reliable source.

Depending on the subject, searching google books is also helpful.