I've finally found the mechanical pencil that can take the brittle Pilot Color Eno pencil leads.
That's the Staedtler Mars Micro 775 Mechanical Pencil which takes the 0.7mm lead.
Previously, I was using the Pilot H-327-L mechanical pencil. Somehow, it would always break the lead while it's inside the pencil. I suspect it's got to do with the stronger spring, or the way the pencil is constructed -- happens to both that I have. Normal graphite leads are fine though.
The spring for the Staedtler mechanical pencil feels smoother to push. It feels good. There's a bit of rubber at the front, and it has a needle point tip.
When the artwork is scanned, somehow the light blue pencil lines won't be picked up by the scanner. The picture above shows the unprocessed scanned image. The grain of the paper is picked up, but not the light blue lines. How convenient.
Using traditional graphite lead means that you would sometimes have to erase them before scanning.
Search for this product at Dick Blick Art Materials.