Places to source picanha (top sirloin cap)?

Hi everyone, I moved here recently and I'm looking to maybe get my boyfriend some picanha; he told me that it was one of his favorite cuts, so I want to try and source some for a belated gift. I've never shopped for any steaks before, let alone what seems to me to be a "fancy" cut (prior to moving, my family simply paid for a quarter cow and had it delivered), so I'm not sure where I could find it. If it's sold in some larger stores, I'm more inclined to purchase from a local butcher if possible. If there are suggestions outside of Brooklyn, I'm open to those as well! Thank you for any suggestions :)