Your best deal right now is a new pair of Cannondale C2 dual pivots. Great brakes that I've used on more than a few late 80's frame-up builds and they will fit nicely.
Just make sure it's not an ST frame (is there an additional bracket above the rear brake bridge?) because those require a longer caliper, especially if converted to 700c from 27".
Wheel & Sprocket has them on eBay for a price so low I hesitate to mention it here.