check places like midwest photo xchange / pittsburgh camera exchange. they have them sometimes. dagor77 on ebay suggested that he was putting some up soon. if you search ebay - put "plate holder" in quotes, &check descriptions too. i saw some a few weeks ago ..
what kind of enlarger do you use? i made a deep negatyive carrier out of foamcore that worked ok - i use an omega d3v ..
kodak used to make tmax 100 in platesfor photomichroscopy/scientific imaging, but they cost something like 350.00 / 100 plate box