Correct me if I am wrong, but doesn't the Holga take the standard LF back? These are a lot of these around used. Actually for an typical LF there are two types of Polaroid back available. I have both types for my Linhof. One uses pack film of the 664/ 690 type (3.25x4.25 image). The other uses sheet film like Polaroid type 55 or 79. Type 55 is really great, fine grain B&W which produces a negative. The sheet films are 4x5.

Steve Perry