Even though it is getting easier to find these guys, it is still fairly hard as the skill sets are kind of mutually exclusive (as already noted) ... and because there is a training gap (most designers know only the Adobe suite of products (this is the part that is getting better).
I personally think you will find that you have to cultivate this blend of skills and that it may not be found in just one person.
One thing I would encourage you to watch is part 2 of the Hiking Mt. Avalon workshop. This part covers collaboration between the developer and the designer ... and also describes the developer/designer/integrator workflow ... which is a workflow that allows you to cultivate these types of people ... and to just deal with this difficult situation.
I personally think that it is easier to bring a developer closer to the designer world (in order to perform as your integrator/devigner ... because one of the main roles of this person is to understand the platform (i.e. WPF/Silverlight) and how to leverage it to make the designs into real live software ... without harming the design/artistic integrity.
In fact, I am an example of a developer with designer tendencies and often perform the role of integrator. I find myself spending a lot of time with our graphics artists/designers, trying to instill knowledge of the platform into them slowly but surely.
For example, showing them the slider isn't just a static graphic but a living, dynamic thing that can be restyled, retemplated, and have behavior. This is an example of trying to cultivate a designer so that he or she can perform more and more as an integrator/devigner ... and lessening the work the actual integrator has to do ... to the point where the role of the integrator may not even be needed anymore ... or looking at it another way ... having just cultivated a new integrator/devigner.
For the record, I can't stand the term 'devigner' either. I think integrator is a much better description of what the person finds themselves doing (i.e. crossing the chasm between development and design).
See these posts (1, 2, 3) for more info.
Hope that helps! You're not alone in your desire to find these types of people!