For the Legnano at least, I replaced brake adjuster and cable holder on the posterior of the seatpost of the 1961 model. Here's how I did it. In the '80s when Joe Breeze came out with a MTB product called the HiteRite seatpost adjuster, I called him and talked about the portion of the product which anchored the unit together. He said he had some extras of that piece around and sent one over. It turned out to be very close, in fact almost a dead ringer to the piece I needed for the Legnano.
Ken Wehrenberg, Hermann, MO-- a lot of MTB products/guys are very inventive/original