It's a chromed lever made by Dia Compe. As I recall, it took a bit of machining to make it work, but yeah, it was quite pretty.
Ben's Cycles has them:
http://www.benscycle.net/index.php?m...oducts_id=3749
Or njsframes.blogspot.com.
Actually, now that I look at them, they're really just shiny new versions of old school cruiser brakes.