FairFaxx, a dealer on Gunbroker often has or handles Martinis, he could probably find you something. Likewise, the Gunboards.com Martini-Henry forum has awesome folks that often trade around rifles if you're in a buying mood.
And lastly, and most awesomest, Martinis are antique. Find one in Canada, find one in the UK, find one in Oz, and you can have it shipped to the US with no paperwork on this end, and unless I'm mistaken, I don't think there's necessarily paperwork on the other end either.