What examples can you find in lincoln’s address of organizing ideas into groups of three?

I'll assume you mean Lincoln's famous Gettysburg Address.

From that address, here are some examples of organizing ideas in groups of three:

The main example is the overall 3-part outline of ideas in the speech.

Another example of three-part statement of an idea comes in the third and final paragraph of the speech.  Lincoln said, "In a larger sense, we can not dedicate -- we can not consecrate -- we can not hallow -- this ground. The brave men, living and dead, who struggled here, have consecrated it, far above our poor power to add or detract."  Notice how Lincoln uses three phrases to emphasize the idea that any words spoken were not the true honor of this place, but the valor of the men who gave their lives there that had already hallowed the ground at Gettysburg.

missouri compromise of 1820 which prohibited slavery