I recently bought a clock for my 2014 America and I thought I'd share the experience. I have no affiliation with the company, but they showed good customer service and I like to reward that kind of thing. I got a clock from clocks4bikes.com. It is a stem-mount clock, as seen in this picture:

When I originally received the clock, I dropped it and, while trying to put it back together, damaged it. I emailed them to ask how I was supposed to put it back together correctly. I did not ask for a new clock and I said I'd be ordering another one. However, they responded very quickly answering my questions and said they'd send me a new clock free of charge. Sure enough, a few days later I received a replacement from them and that's the one you see in the picture.
So, if you're looking to add a clock to your bike, I highly recommend clocks4bikes because their customer service is excellent and the product is also extremely good looking.