I'm down in the Baltimore area so I know a number of shows in the general area.
As uglybug mentioned,
NOVA Open runs a show in DC each year, though the show is at the end of August / beginning of September. This is going to be a show similar to games day where you have a bunch of gaming competitions plus a painting competition. The painting part is relatively new, this was only their second year doing it. But they've got some great sponsors and awards including a bunch of stuff from Secret Weapon and some Grex airbrushes. They're also a Crystal Brush qualifier, so whoever wins best in show will have CMON fly them out to Crystal Brush. Oh, and they typically offer a number of seminars for various painting techniques which is pretty neat.
There are also a number of purely painting shows including the
Long Island show (Nov 16), the
NCMSS show (another DC show in September), and
MFCA show (just outside Philly in May). Now these three shows began from historical painting clubs, so they run a little differently from a GamesDay type show. You'll have a mix of historical and fantasy/sci-fi figures, often with larger scales (54-90mm). Judging is done on the open system, so each piece is judged against a set standard as opposed to a straight 1st, 2nd, 3rd where you're judged against other entries. As a result every entry that merits a gold medal gets one, same for silver and bronze. These are purely painting shows so there aren't any games going on, but they will have a decent sized vendor area. I'm not sure how close to Philly you are, but the MFCA group holds monthly meetings. It might be worth checking them out sometime.
Alternatively there's
JerseyFest in September (busy month). This is more of the vinyl and garage kits, a lot of movie monster style stuff. They also offer a few short courses.
And lastly there are a number of
IPMS shows. This is an international plastic modeling group, so the focus is more on vehicles but they often have figure categories as well. There are local chapters all over the US with multiple ones doing shows in the PA, NJ, MD area.