I found a Beseler opaque projection lens on ebay, and clicked the "buy it now" button. It has a 5" aperture, and 18" focal length. That should be plenty enough to grab the faint stars.
I don't imagine it has good color correction, but at 480mm, this might not be an issue.
How would I go about finding the image circle when it arrives?
Aim it towards the sun and a white poster board?