Honestly, I suspect you'll have to do a lot of research into this and make one of your own from scratch.I don't know if any of these Google Links will help, but it can't hurt to look. If need be, you can refine your search perameters.
Fancy Dress! Adam, if you're in the UK be mindful of the law (I can't cite it as I write) that proscribes the wearing of MN uniform in an incomplete or disrespectful manner or is otherwise likely to bring the service into disrepute.
Having said that, in today's climate I think you'll be fairly safe!