The C700 and C760 Dichroic Heads are the same, only difference is the numbers they put on the front.
The 6x7 chambers can be hard to find. I looked for a long time before I found one.
Look for the whole head and ask if the chamber inside is a 6x7 or 35mm and if 6x7 then you could just buy the whole head as they sell for next to nothing; I think I got a spare head for about $15. That way you will get a 6x7 chamber, a spare bulb and a spare head.

You can still find the chambers new, but they are about $70.

BTW, the C760 Negative carries are different than the C700.