I don't have any personal experience with traveling, but I have noticed over the years that there are at least a couple travel agencies that always advertise in the "classified" sections of the nursing journals that they specialize in psychiatric travel assignments (the ads have always caught my eye because I'm a psych nurse). Of course, now that someone's actually
asking, I can't think of the names ...

I'm sure you could pick up a copy of any of the general-interest nursing journals (AJN, Nursing2008, etc.) at work, or do a web search, and find them. Good luck!