i've had a chance to use a metal lathe here at Smithsonian for a couple hours. one of my first projects has been to make blanks for centerpull pivots.
material is 1/2" solid mild steel rod. other than fractional drill bits and a lathe, all that's needed is an M6 x 1.0 tap and the requisite tap handle and tapping oil. also you'll have to replace the brakes' stock buttonhead M6 bolt with one that's threaded over its whole length. 25 mm is probably long enough.
chuck the stock into the lathe. set it spinning at around 1200 rpm. face the end. use a centerdrill to start a hole. drill to a depth of 9/16" with a 3/8" bit. switch to a 13/64" or 5 mm bit and drill to a total depth of over 1". now cut off at 1" from the end where you started drilling, face the new end, chamfer/deburr all around. tap the end with the 13/64" hole.
so now you have what amounts to a sort length of 1/2" OD, 1/16" wall steel tube with a thick-walled end to support the centerpull pivot and provide a hole for the appropriate bolt.
miter the thinwall end to fit your seatstay or fork blade, and braze it up, using the stock yoke as a guide for how to space them-- around 65 mm i think.
i made a sample pivot and brazed it to a scrap fork blade with a small brass fillet. it's kinda tricky because the dang thing is so small, so i had to turn it over like every few seconds. then i grabbed the pivot in the vise and tried to break it off by cranking on the blade...no luck whatsoever: the pivot wanted to deform before the braze began to budge.
at least through May 2007, i can make these pivots pretty easily, so if you need a couple pairs, email me and we can probably work something out.