The question about the Cinelli "Riviera" frame came up in the UK a couple of years ago, and at that time the Cinelli model became confused with another "Riviera" frame that had been imported into England in the 50s. This latter was only available in 22" and in yellow. No other choice appeared to be available.
That there was a Cinelli "Riviera" model is not really in dispute I think, but I wonder if anyone knows who actually made it. Was it a cinelli produced frame or was it bought in? I think it is widely accepted that many of the Italian builders helped each other out with production at busy times and shared manufacturing capacity, and it is not uncommon today to find a number of small brass foundaries all producing bathtaps for a larger "brand".
The "Riviera" on eBay is virtually identical, lugs, drop-outs, seat cluster etc, with a couple of Fiorelli "International" model frames that I own. However the explanation, rather than looking foa a conspiracy, could just be that in the 50s the Italian builders had only a limited amount of frame component suppliers to buy from, leading therefore to most frames looking the same. Italy wasn't alone in this problem.
Just a thought on a very sunny but very cold (for England) day..
Norris Lockley