Any tips on getting used concrete chunks/slabs?

Hey all! My fiancé and I are hoping to build a retaining wall at our home and LOVE the idea of re-using salvaged concrete to do so. We try whenever possible to reuse salvaged materials vs newly created for both aesthetic and environmental reasons. As I understand it, concrete is also difficult to dispose of so in theory this should be a pretty cost friendly solution. I’m wondering if anyone has any tips on where we should hunt around to find a source or has experience in something similar? Thanks in advance!

(Oh and we’re in the New York State USA region)