I finally received replies from Dahon. I explained to them that my local bike shop doesn't carry anything made by Dahon and I had no other option than buying online. People in my city buy everything from toilet paper to BMW online, so why not Dahon?
Dahon California rep refused to send any part to me directly, and insisted to ship parts to a bike shop, at my cost, although the problem occured due to imperfect design which they recognized and redesigned.
So, if anyone buys a new Dahon, my recommendation is to tighten screws for seatpost pump, magnetix latch pieces and other things that are specific to Dahon bikes on regular basis to prevent parts fall off during normal riding. My air pump screw fell off on day 3, magnetix screw and spring (from the rear part) fell on on day 4, of normal light riding after buying this bike. I may use Loctite at those places if the screws become loose again.