If you want to sell more than 1 of each type of product through Cafepress, you can do it by having more than 1 store, each store containing 1 of each product type. You can combine these so that the customers see 1 big store containing all your products.

Use a URL like this:

http://www.cafepress.com/cp/store.aspx?s=mailscanner,mailscanner2

This will display a store that combines all the products from the "mailscanner" and "mailscanner2" stores.