warranty option
Here is another option. I worked in a bike shop in college, and was incharge of warranty claims. Each manufacturer is different, but it comes down to the shop employee being able/wanting to maximize the deal for you. In the case of a frame as old as yours, Bianchi will offer you whatever the largest size was in a similar style bike. If it was a mid range bike, then expect a mid range frame.
Several times the guys working in warranty on the manufacturewr's end were willing to totally hook me/the customer up. If the guys at the local shop are cool, and not super lazy, you should be good to go. Expect to have to pay for the bike to be reassembled,cables, housing, stem, headset, etc...
It is only the frame that is covered in the warranty, so because your bike is so "vintage" expect to incur some compatibility issues.
Another option, which you may need to
ask about, is that in cases like these, Bianchi may offer (or be willing) to sell you a complete bike at a highly reduced price; wholesale or less, typically. Shop employeez are offered 2 bikes per year at 20% under wholesale, so it's not a unrealistic to have this deal "extended to a loyal customer of the brand".
It usually works out pretty well, but I did it for a few years, and was pretty profficient at "working the system".
Worst case, you get a new frame and fork and have to do the
ebay thing. Realize also, that companies change their geometry every could of years, and the manner in which the frame is measured can differ as well. Bianchi has evolved into larger geometries since your bike was built, but it's Italian, so expect a taller frame with less length to be the general proportion.
At 6'5", I can ride the largest bianchi frames, but prefer someting with a longer top tube, because of my torso length, but it's do-able.
good luck with it either way.
Wc