The PRO-97 will also serve you well in the realm of milair, of which there is a TON in the DC metro area. To get just a small sampling of what you can hear, go to the Sticky Thread for Milair in the Maryland forum.
There are no stores, apart from RS (which I wouldn't trust further than I could throw an employee), that do programming for this area. You didn't say anything about what software you are using, and what specifically you want to hear. Without these two very important points, no one can really help you with files. There's a ton of stuff to hear in the DC area - you need to be much more specific. You're really going to need to become more familiar with programming your own radios, but that's just my opinion. There's enough help in the wiki and here to get you started (even with getting a file from someone), but learning it yourself is where the real education gets done.
As for programming the DC 460/800 mhz system, here's a wiki article that covers that subject...(look at the technical notes section for a couple of tips)
Programming the MPDC in Digital Scanners - The RadioReference Wiki
I'm sure we have more than a few of the GRE/RS digitals in the area to help out with that. There's also the Scan-DC group on QTH.net which is quite active.
best regards..Mike