I know that the Great Gatsby has numerous uses of irony but I am looking for a specific quote that demonstrates irony. Can you help?

Here's another for you.  In Chapter 8, Nick (speaking to Gatsby, then internally) even tells the reader that he is speaking ironically:

“You’re worth the whole damn bunch put together.” I’ve always been glad I said that. It was the only compliment I ever gave him, because I disapproved of him from beginning to end."  First he nodded politely, and then his face broke into that radiant and understanding smile, as if we’d been in ecstatic cahoots on that fact all the time.

Furthermore, you might consider the title itself as ironic.  Gatsby is hardly great in any way; even his wealth is ill-gotten.