Well, I was sitting on a barstool, talking to the gentleman next to me and he used the phrase. It tickled my fancy, so I wrote it down on the back page of my address book. I asked Professor May how it was spelled and he liked my spelling for it. I also asked him exactly what it meant and he sad "Plum out of the county an' n'elly out of the state".


I also found this example and alternate spelling googling:

We went to the Plumb Nellie Crafts Festival in downtown Branson. The Plumb Nellie Festival got its name from an old British expression: you can find "plumb nearly anything" at county fairs. While the "nearly" in this phrase was Americanized into "nellie", the meaning of this still remains that you can find truly nearly anything at the Plumb Nellie Crafts Festival.
This came from a Missouri state website. There are also references in North Carolina, many references in Georgia, including a word of mouth definition here: http://www.onlineathens.com/stories/012002/ath_0120020007.shtml
And then I found this blast from the past, a band I never heard of: http://www.johnearlwalkerband.com/plumnelly.html
I'm sticking with "plum n'elly" 'cause I like it