Unfortunately it is not possible to simply duplicate or copy an existing card design; this is largely driven by how all the program logistics are defined when you activate your card. There are a number of parameters that cannot be exactly the same - so there really is no way to simply 'clone'.
Given that you already have images, and the details of the existing card we believe you can create an 'almost identical card' in less than 10 minutes.
In fact, you can make it even easier by having 2 browser windows open. In the first browser window you click the existing card and then navigate to the card editor (the pencil icon in the left-hand navigation). Then, in the 2nd browser windows you start with creating your new design and you can copy any text and settings easily from the 1st browser window. And then make your way through the entire design and activation process step by step - copying across anything that you want to be the same and altering any information as you need to.