Hi Michie,
I made a similar inquiry about renting a longer lens not too long ago for my ARCA 4x5 FC camera and found that Calumet in SF had a few in stock. They supposedly have a Caltar f 5.6 300mm, a Caltar f6.8 360mm, and a Rodenstock f9 480mm on hand. As I recall, a Friday to Monday morning rental counted as one $30 day. My problem was a lack of rail and bellow length. Good luck.
Roger
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