In the US, Krylon Ultra Flat Black spray paint is a good place to start for paint. You can also find black flocked self-adhesive paper and felt at hobby stores. Either way will probably work very well for killing internal reflections.

Also found the angle of view data, although stated differently by Renner. The image diameter on a flat surface (non-curved film or paper) is approximately 3.5 times the focal length with a good pinhole. One inch of focal length gives you a 3.5 inch diameter circle, so 1.85 inches or 47mm of focal length should give you corner to corner coverage on 4x5.