I don't know how they compare for pricing, but Zappos in the US often has a reasonable selection of Superga sandshoes.
Edited to add: I also remember that a friend of mine bought some from Asos, but again I don't know what the pricing is like. Herringbone also used to stock Superga, although I'm not sure if they still do.
Yeha I futzed around and just went and bought some keds ($20!) - all I needed was a simple white canvas sneaker - superga were the easiest until they were sold out. Appreciate the thought though JM!