As I understand you, you seem to be wanting to produce a contrast reduction mask for your negatives. The material that I have used is APHS film from Freestyle Photographic. It comes in 5X7 size and is orthochromatic. Additionally, as John has indicated a similar material is available from Photowarehouse.

My records indicate an exposure time on unsharp masks of appr 16-22 seconds at F8 with my Saunders 4550 VCCE enlarger with the head at 8X10 enlargement projection. Keeping in mind that this will vary with original negative density and the fact that I use Duratrans diffusion film as the means to produce the unsharpness in the mask. The density of that material would need to be factored into the exposure time if one wanted to produce a sharp contrast reducing mask instead.

I have used dilute Dektol 1-30 for producing low contrast and low density unsharp masks. I have used Dektol 1-10 for producing shadow enhancement masks.

Good luck.