8X10to 5x7 reducing back for C-3 Calumet

Hi, I am trying to find out if the C-3black} Calument 8X10 Bi-camera can be fitted with any make of reducing backs . I will need a 5X7 back for it. I called Calument and they said I had to buy the frame and the spring assembly for the 8X10 to 5X7 back. $499.00+359! {new}see what I mean? That will cost more than the camera. So if any of you know of other different makes {used} that would fit please let me here from you. Thank you, Dan

I assume you mean the C-1 8X10 by Calumet. I too search a long time before finding one on ebay. I paid $55, they do exist, try calling some of the larger used camera stores in Shutterbug magazine. Or like me, linger over the LF pages at eBay