The original idea was described in a post on Thorpe’s blog in September 2012 called “Eureka! – replace the Euro with the N-Euro”
A 13 minute Youtube presentation of the N-Euro idea can be found here.
N-Euros were also mentioned in a 1 hour talk that Thorpe gave at the Tououse School of Economics in February 2015. The complete presentation, called “Fixing the Economic System” can be found here, and the part concerning the N-Euro starts at 49:37.