i'll join the club!
i received a package yesterday from an antiques dealer in new jersey. she had listed an esterbrook mammoth falcon box in fair-good condition, containing an assortment of nibs. i took the chance and ordered.
the box is indeed a 340 mammoth falcon box. other than a few small stains here and there and a small corner of the glued on label lifting from the bottom, it is in quite good condition. upon opening, i found a few nibs alright - 340 mammoth falcon nibs - 29 of them!

one thing i discovered that brian did not mention is that these nibs have a nice amount of flex and seem very smooth out of the box.
now i have to emulate his search for the elusive mammoth pen holder. by the time i find one, i may have figured out how to use a digital camera to the point of actually posting a photo.
they're still out there, folks, just have to keep looking.
thanx