The situation here with sitall is as follow:
Sitall are making in a town near Moscow. Now the optical factory have almost stopped to produce it mostly due to financial problems. Also there is an order of the director of the factory not to sell just optical materials but complete set of optics. The official price for sitall now is about 45 $/kg (this is about two times less then for Zerodur).
In principle I can help to you to find out a blank your friend need. There are small optical workshops which have blanks like this and are ready to sell it for a price not higher then 45 $/kg. And I have access to these firms.
I guess same problems may arise to get permission from custom office for export license.
In any case, let me know if you and your friend will have decide to buy.
Best regards, Alexander Yascovich yas@hea.iki.rssi.ru