I was looking at something similar for the Roadster and I came across these which I thought looked quite period and more importantly..... cheap!
This one is for the series 3 Lambretta but they do different sizes and designs for the series 1 and 2.
Not exactly sure of the overall sizes but at that price it is probably worth a punt.
http://www.ebay.co.uk/itm/LAMBRETTA-...item48839341fa
