Until you can find the "real thing", you might be interested to know that SAKAE copied EVERY seatpost imaginable in the 1970's, including simplex :
http://www.asahi-net.or.jp/
The APEX model is virtualy identical to my NOS simplex fluted alloy post. I have one of these (its an earlier one with flourishes and CUSTOM on the front) on my raleigh gran sport.
- Don Gillies
San Diego, CA