Where we can find the American dream in The Great Gatsby and Of Mice and Men?american dream in these works

Concerning your question about the American Dream in the works you mention, The Great Gatsby and Of Mice and Men, you need look no further than the main characters of each.

Jay Gatsby is the embodiment of the American Dream.  He makes good, so to speak.  Born into a relatively poor family, he achieves wealth, apparently, by hard work and entrepreneurship.  He is a self-made man.  He owns a mansion and has the finest shirts Daisy has ever seen.

In contrast, George and Lennie are seeking the American Dream, but will never achieve it.  Their attempts to raise a stake, as they say, never amount to much.  They would like to own their own place and raise rabbits, but it will never happen. 

Gatsby achieves the American Dream, but the dream proves hollow.  George and Lennie dream about wealth, but will never achieve it.