I looked through John Vogt's 30" f/3.3 (sagged 'egg-crate' mirror) at Stellafane (1988? 1987?) and it was marvellous with a 20 mm Nagler. I think you should get in touch directly with the people who have built these things. It is probably 1000 times more dificult to build than an ordinary scope.
Look for Phil Harrington on the 'net, he lives on Long Island, as did John Vogt.
There have been articles in Sky and Tel over the last 10-15 years about this subject. Some manufacturers offer these types of blanks, but I don't know which ones.