I believe that the only chimney finder Rollei made was for the SL66 camera. I have one and it did not fit my 2.8 'flex. In Irving Penn's book "World's in Small Room" there is a photo showing Penn's Rollieflex with a chimney finder. It is a Hasselblad finder which was adapted to fit the Rollei.

Cheers
Morry Katz - Lethbridge