Like Barry, I've used Fuji MI-DUP duplicating film. I bought it from zzmedical. I develop it in the print developer I usually use (Ilford PQ, from the recipe Ian Grant has on this site). It needs exposures from 2-8 minutes, usually. With experience, you can get the contrast right by visual inspection during development, since you can develop it in a tray with a red safelight. This works well for making enlarged negatives I've used for Kallitypes and cyanotypes.

Mark