I think this is what you want for a fixed folder http://www.foldingbikes.co.uk/xootr_swift.htm assuming you can get hold of just the frame. As used to win the Smithfield Nocturne folding race IIRC. You could also do the magic gear trick on a Dahon - mine (a Helios SL) is several years old now and holding up OK, but you might be better off trying to find one of the steel-framed models.
I think this is what you want for a fixed folder http://www.foldingbikes.co.uk/xootr_swift.htm assuming you can get hold of just the frame. As used to win the Smithfield Nocturne folding race IIRC. You could also do the magic gear trick on a Dahon - mine (a Helios SL) is several years old now and holding up OK, but you might be better off trying to find one of the steel-framed models.