Tracy Storer hangs out on the LF forum at photo.net (soon to reconstitute itself over at largeformatphotography.info, by the way). He handles one of the Polaroid cameras available for rental. I think they're in New York, San Francisco, and Boston.
That is good news on the LF forum. With the switch to photonet it lost a number of long standing contributors and a more congenial, collegiate feel. At the LF photography web site is where it belongs.
David is correct about the locations, although I believe that one of the cameras is sometimes transported to different locations for various events.
There was a pretty in depth article in View Camera a couple of years ago, about Tracey and others who run the camera. If I remember anyone can schedule a time to use it, and that includes technicians to help with lighting and the camera operation. I don't know if the article mentioned the cost, but the number $200 an hour seems to stick in my head and I believe that incuded materials.
David, perhaps you know the amount and details better then I can recall.
Polaroid does supply material for their 20X24 camera.
Additionally, Polaroid also supplies 20X30 material for Joachim Knill's homebuilt camera. (View Camera Sept/Oct 2002)
Knill typically uses 8 inch (200 mm) and 12 inch (300 mm) process lenses on his camera. Now that is some serious wide angle considering that 37.5 inches or 952 mm would be a normal focal length for that format.
Art is a step from what is obvious and well-known toward what is arcane and concealed.
Not sure of the cost. I just skimmed the article in the Polaroid issue of _VC_ mag (sept/oct 2001) and didn't find it, but I know I've seen it somewhere. I don't think there's much reason for Polaroid to list the materials on their website, since the market is so small. Anyone who needs 20x24" is probably on a first-name basis with the Polaroid folks (or they ARE the Polaroid folks).
You can also shoot 20x24 B&W. Wisner makes a camera with a standard back and I think S&S makes the holders. $9000 for the camera, $600 for a film holder and $350 for a 25 sheet box of HP5.
or another way to look at it is about $163 a lb at 55 lbs.
I have drawn up plans to build such a camera that would weigh about 30lbs., have full front movements and rear tilt and swing. It is contained in a clamshell design that provides the camera bed when opened and protection for GG and film and holder(s). It would have 40" of extension so it could handle a 36" Turner Riech lens and several Goerz Apo Artars that cover 20x24. But for now the drawings are on the shelf for lack of time. But someday....
I've seen a Lotus 20x24". It was a studio model set up on a kind of rolling stand, and I think it had motorized focus. Really a beautiful thing, and the owner (from whom I bought my 11x14" camera) had a hot light studio.
I've seen Joachim Knill's large Polaroids at the Fort Worth Main Street Arts Festival. Gorgeous stuff. He constructs elaborate still lifes with items seemingly suspended in air and emphasizes the almost surrealistic effect by using camera movements for selective focus across disorienting planes. If I could afford to collect fine art photography some of his work would be in my collection. It's so different from anything I do that I'm not tempted to analyze or figure it out - I just enjoy it.
BTW, Knill built his own camera. He includes a photo of himself with the camera in his booth displays. Unfortunately it's impractical to actually lug the camera to these shows - I bet that'd draw a crowd.