Warning: Period Tire Nerd AlertI was recently in the same position. While I've always loved the period Michelin X, XZX, and XWXs, the prices are now simply ridiculous. I did A LOT of research on period tires, including looking at Pirelli Cinturatos, which were recently reproduced. Sadly, they are very expensive as well.
I ended up buying Vredesteins, based on the strong recommendations of the Porsche 356 and early 911 guys.
http://www.universaltire.com/vredestein.html165s
Notice the great, vintage looking tread pattern.
For the price of buying one
PAIR of Michelin XZXs, I was able to buy
FOUR Vredesteins, plus shipping, plus take my wife out to dinner, plus retire earlier

Early impressions:
- They look good and period (no "square shouldered", low profile look of modern tires that I detest on vintage cars)
- Great ride quality
- Great handling
Make sure the you get the
SPRINT CLASSICS,
not the standard Vredesteins.
I ran Nakangs 15-20 years ago and hated them, as they wore out incredibly quickly. And it wasn't because they were a sticky compound - their handling was nothing remarkable - and simply wore out earlier. They just looked and felt cheap, IMHO, and were scary in the rain!
My 1.5 cents.
JP