The negative carrier is the Femoneg. With the glass inserts, it handles all formats and you don't need anything else. You can also get metal inserts with holes (Femomasks), each for a specific format. Some versions of Femomasks have spring loaded alignment pins, so you can use a plate on the bottom and glass on the top.
Another source for parts and accessories is direct from Durst -- http://www.durst.it/ and click on "Online Shop". The prices for US & Canada are similar to new prices when Jobo was the distributor (=expensive), but at least include shipping.
Focal Point ( http://www.fpointinc.com/glass.htm) supplies non-OEM glass for the Femoneg.