This will sound stupid, but have you checked with your Merckx dealer? I got a carbon Merckx seatpost that is sensational. If you LBS doesnt stock anything call R&A here in NY. They sell more Merckx than anyone in the US.
I like Thomson's clamp the best, but FSA has more setback and is pretty cool. Both avail in 31.6 - check the Merckx page to make sure before you buy - or have a shop verify with a shop post.