Yes, I have the Polaroid Land back for my RB67, it takes the Fuji instant FP100C and FP100B films.

Current new ones from Mamiya:

http://www.mamiya-usa.com/rb67-pro-s...ck-holder.html

Or get a used one. Check the compatibility chart for older ones, I have the Pro S
http://www.reznitsky.info/Mamiya/Comchart.htm