Click on Wiki at the top of this page, enter Potomac TRACON in the search box and that'll take care of half of what you need. All the Potomac TRACON freqs are there - both VHF and UHF - and they are broken down by airport area.
For Patuxent freqs, go to the Maryland forum, click on the thread "Sticky Thread for MilAir II" and scroll down through the messages. I recently posted all the Patuxent freqs (along with Giant Killer, etc) as part of a series of posting all my MilAir bank frequencies to that thread.
I don't think Patuxent is part of its own TRACON - I could be wrong about that...anyway, we have a Wiki page that's also devoted to that. It's more than a little dated, but it would be a place to start. I really need to use Tin's list to update it...
 While I don't have the Pax freqs loaded, I do have the Potomac TRACON freqs loaded in a spreadsheet. Send me an email at email@example.com telling me you want the Potomac TRACON list (in what format, please...csv, spreadsheet, ARC250, others? - I'm afraid I don't have any RS gear, so I can't supply a .p9x file, sorry)
Mike, I didn't know Patuxent had it's own TRACON either but then ran across a reference to it in the new IFR Supplement. I think it's in the section that describes the three helo operating areas at Pax and the freq assigned to them.