Someone asked me to do this cake for a baby shower. I know how to make the bow/ribbon, but how do you get the polka dot pattern on it? Do I need to buy some sort of impression mat? If so, where can I buy this particular one?

Also, see the top edges/border how it goes up & down? I hope I'm explaining it ok. How can I do this?

http://i42.tinypic.com/14tbg28.jpg

You can get the pattern on the bow with an impression mat or an impression roller. The top edges of the cake are made from a crimper. I've seen them on Global Sugar Art and Sugar Ed Productions.

I agree that the bow is done with an impression mat or roller, You could also cut the fondant with an endless cutter http://www.globalsugarart.com/product.php?id=18942&name=Endless%20Frill%20Cutter%20Set%20by%20Orchard%20Products
and then wrap around the cake.