Thanks for all the great ideas and feedback. There are some really innovative ideas here.
You don't have to talk ME into making an arrangement for getting coffee grounds from a local shop. I already have one. Coffee grounds are amazing! There are never enough, though...
Collecting free waste materials (aka scrounging) is obviously an excellent solution in many cases. Unfortunately, for many of us, logistics and practicality limit our ability to take advantage of many potential sources of nitrogen. There is the matter of time - not so much that it takes time to collect materials, but that those of us with 9 to 5-ish jobs and long commutes and the usual round of other obligations just aren't around at the right times or consistently enough to take advantage of many sources which would be viable for others. There is also the matter of transportation. What one can easily transport in the bed of a truck doesn't necessarily work so well in the trunk of a Subaru.
It's also important to consider that not all stores are created equal, and by taking care with where I purchase, I can support selected local businesses. I consider every dollar spent at my exceptional local garden center a good investment into the future health of my community and my garden. They stopped selling things like big sacks of alfalfa meal long ago, however, as there is effectively no call for that around here. Fortunately, they pointed me toward a real feed store about 45 minutes away that stocks a lot of what I might be looking for and can order in other items as well.
Ultimately, I may or may not choose to bring in a store-bought material, but you all are providing some excellent food for thought.