I have two Norita 66 bodies and a pile of lenses (I don't have a 240 or 400, but I would looooove to) and I am always searching Ebay and so on looking for bits for them. They're very rare anyway I haven't seen a metered prism show up anywhere in a LONG time. In fact, I bid on a waist-level finder a month or so ago and was completely gobsmacked when it sold for USD $225!
I use my waist-level finder more than even the standard prism because it's amazing for street photography and I have a couple of excellent hand-held meters that do me just fine -- a Weston and a GE, neither of which is battery powered and both of which, in spite of being really old, are really accurate even in low light.