Aware that this is a way old thread but my recent experience with a broken latch on my Dahon Boardwalk's folding mast is relevant to this topic. The bike shop who are Dahon dealers identified the broken piece as a "Quill bolt" which was 1/8 inches shorter than the one Dahon now carries and he thought that no replacement could be found. I contacted Dahon and they said I need to ask my Dahon dealer to order Dahon part number H350P30 which turns out to be the entire latch assembly on the folding mast - the part cost $12 from Dahon, the repair cost $12 and it worked!

So don't throw that old Boardwalk away till you've gone to the ends of the earth or at least had an email exchange with Dahon about the dilemma.