You want to get a Regina America 92 Superleggera - Aluminium cogs, light as anything, but wear out really quick. Come up on ebay from time to time or you can get one from www.sjscycles.co.uk
. They are listed as non index but you can just about get away with it.
Or just look out for any of the Regina lightweight range. The Regina syncros were the index specific ones but I'm not sure if they did a Regina syncros superleggera, maybe some one else knows?
SJS Cycles could not deliver the aluminium model. Out of stock...... for good! ;(