they must be using thicker sheets of metal since the last time i got metal from them
i had no problems inserting the black sheets into my regular old film holders.
in addition to the video ( above ) you can hunt around for old 4x5 plate holders
and cut the septum ( like in the video ) you won't need silver wire, just leave a border on your SG tintype
take the spring out of the bottom and just put a sheet of cut glass against the back of the coated tin to apply
pressure to it ( you could probably use a bowed piece of aluminium make a light metal spring to do the same thing).
the pack film adapters i mentioned previously make this ez
https://www.ebay.com/sch/i.html?_fr....TRS0&_nkw=graphic+film+pack+adapter&_sacat=0
and they sell for less than a plate holder that you will have to cut up/destroy but still you only get 1 exposure.
you can buy a falling plate camera and use it to shoot your tintypes
https://www.ebay.com/sch/i.html?_fr...amera.TRS0&_nkw=falling+plate+camera&_sacat=0
just use a sheet of matboard to take up the space where you put the plates ( or coat glass instead of metal to make SG ambrotypes)
i have and use something like this
http://www.ebay.com/itm/Rare-Antiqu...887690?hash=item3d45f8070a:g:ldYAAOSwn5RZjLp7
its not rare but its old ( this is a # 5 ) the #3 is hard to find and not as nice, but all the others ( 4x5 and 1/4 plate size ) are plentiful
and usually cost much less than 100$ ( the cost of a few plate holders and the time to modify them )
good luck !
john