Did some quick searching and also didn't turn up much vectorwise. If you are a member of the NPMA, I found they have a logo page, but you're most likely best off contacting each area and asking.
I've had to contact people before for benefits and usually the companies/branches are fairly open. "Hello, I'm soandso with suchandsuch and I've been asked to use your logo for a sign for an upcoming event" kinda thing. Worst thing that can happen is they tell you you can't use their logo which may have become an issue in the first place. Sometimes you don't always get what you had hoped, I got some jpegs before via e-mail, luckily they were of high enough quality to trace.