The Batgirl Beyond arc is collected in print today! BATMAN BEYOND UNLIMITED #18 is in stores now.
If you want digital copies, however, those are in Batman Beyond chapters #27 - 29. 27 is currently available and the last two chapters will roll out soon.
For those interested in process and unnecessary references to stupid things, here are some interviews! Here's one with DC Women Kicking Ass, where I also briefly discuss Hawkeye, and one with Project:Rooftop, which has exclusive sketches. Below, the cover sketches I submitted before going to final with the fourth.