Re:
I love me some Retro Cyclocross (just cyclocross bikes in general really). Lovely, elegant to look at and more versatile than a
normal road bike.
I rode a bike I'd had resprayed as a Flandria in the Eroica 2013. It was very pleasant, the better braking
from the cantis and the bar end shifters made it a bit more comfortable and easy to ride than a normal
vintage road bike.
There is loads of room for fiddling about with weird set ups too, single chainrings, cables routed through the
stem/seatpost, different gearing, drillium...
The most obvious brand to look for is the aluminium ALAN/Guerciotti bikes from the 70s/80s. Relatively easy to find, and
nice and shiny with the anodized frame and lugs you can polish up. The frames were very flexible which is why they wer popular for cyclocross. Main problem is that the frames could crack, e.g. I had one where the headtube cracked because of a badly installed headset.
Apart from ALAN, you have Empella )(Netherlands?), Diamant (Belgium) and a few others. Ritchey made the legendary Swiss
Cross, which is my personal holy grail bike.
Main thing to look out for is that cross bikes are basically ridden abusively: rust, cracked frames, broken stays, ovalised headtubes and so on are unfortunately more common because of the hard life a cross bike is subjected too, so be careful when viewing a bike to check it carefully.
Riding wise, if you go for proper vintage gearing, you'll be getting off and running more often. Vintage cantis can be a bugger to set up, but steel forks seem less likely to suffer shudder than carbon ones.
Hope that helps,
Good luck,
Johnny