Those "surplus's" are your best bet local, I know there are also some sold online by folks that deal in them. No matter where you go, they wont be cheap, unless you find an individual with one to sell.
I had a GP 18' diameter tent for many years, the quality is insane even in a 1948 model, but an outfitters tent may be easier to get. I almost got this one before we bought the toyhauler, great reviews and nice for the $.http://www.amazon.com/Kodiak-Canvas-Flex-Bow-Deluxe-8-Person/dp/B001NZWQ1C
Or, look into a Yurt style tent.
No cheap way out though.