Homebrew PCBs

Since Kepro went out of business, I need to find a new supplier of
presensized negative acting photoresist material . I tried some positive
material from Injectorall, but can't seem to get a decent board from it. I'm
sure it will work after I figure out the correct process, but that can get
pretty expensive.

Ideally I'd like to find some place that provides the same type of material
as Kepro had. It was a 1.3mil thick laminated negative acting photoresist,
Riston EM312 Photopolymer film made by Dupont. It was developed with sodium
carbonate.

Any ideas
Ron