Most likely E-Bay, but have not seen one in awhile. And the last set went pretty high. And it's B-26K or A-26A, (Counter Invader or Nimrod). I prefer the B-26K Counter Invader nomenclature over Nimrod. Besides The Royal Air Force has a Nimrod for Maritime, ELINT and search air rescue missions. Hopefully Cutting Edge may come out with a 72nd version of their 48th scale set. Other than that or post a want ad at the various modeling sites. Some of this stuff is hard to get.
I run into some unusual stuff. If I come across one I'll be sure to let you know.
Chuck
Fly Navy