Well, most exotic but recognizable flowers can still be found in florist shops just about anywhere, regardless of their native habitat. Orchids, for example, are a symbiotic species of flower that naturally grow only in the crooks of the upper branches of rainforest trees. Many plant nurseries, however, have special humidified greenhouses to grow them in far more convenient locations. So, you could go to, say, Brazil, and carefully fly through the rainforest's canopy until you found a particularly beautiful orchid, and then carefully take a few of its blooms. Or, you could walk a few blocks from your house, find a decent neighborhood florist, and buy a carefully cultivated specimen that looks pretty much identical.
Similarly, my flower of choice would probably be the Bird of Paradise, a plant native to the tropics and nearby regions. Although I have seen them growing outdoors in Florida (like many plants, they're not native to the area, but they can grow there), they'd never be able to survive here in New Jersey. Still, I can buy them easily enough from a nearby florist.
If you're going for a motley bouquet (which would have to be very carefully arranged, so as not to clash), I'd personally say that you'd have to include some Gardenias in the mix. Small, delicate, and unobtrusive, they give off an absolutely delighful fragrance. Similar to Jasmine, actually, but somewhat stronger.
On a recent trip to Alaska, I came across Fireweed. It says different things to different people. I don't think it's normally found anywhere else, but there, it's common enough to have earned the name "weed." To some, it's a beautiful and exotic flower, one of the few splashes of color in that mostly frozen region. To others, it's an annoyingly ubiquitous weed. I found it charming, my mother thought it ugly. In any case, it's a rare and exotic plant. It might go well as part of a bouquet. It's also one of the very few native Alaskan purple flowers that is edible rather than poisonous.
A search for pictures of the plant proved difficult. Most sites want to show a close-up, which doesn't really give you a good idea of what it looks like to most people.
This is about the best I could find.
Searching around, however, showed me
this page, which has a listing of many types of flowers, some of them quite rare. The site started out as a listing of plants native to upstate NY, but it now includes information about Fireweed and Jewelweed, among others.
Going back to he first site, I browsed the pictures of Alaskan flowers and came up with the Alaska state flower. It might be appropriate for you, or it might just bring up unpleasant topics. You'll have to think about this one yourself and decide which it means to you. The flower is, of course, the
Forget-Me-Not. Other than that, I can only suggest a trip to a botanical garden. Walking through their exotic greenhouses, you can find many rare and beautiful plants, often from around the world. Generally, they won't be the sorts of plants you'd be able to find at a florist's shop, either.
If you don't have botanical gardens convenient to you, you could always try online. A search for "botanical gardens virtual tour" turned up several likely hits, such as:
Huntington Gardens The Desert Botanical Gardesn of Pheonix, Arizona The Phipps Conservatory The Selby Gardens (They're in Sarasota, FL. I've toured there myself a few times)
Hawaii Tropical Gardens One last comment. I'm just about alone in this, but I, personally, have never cared for the symbolism of cut flowers. To me, what you're saying when you give someone cut flowers is, "Here. I have found a thing of beauty and cut it from its life source for you. It will wither and die quickly, no matter what you do. Your best efforts will only sustain it for a few days. Enjoy." On the other hand, a well-chosen hardy potted plant can say something very different. "Here. I have found a tiny seedling. If we care for it properly, it will grow and flourish. It can last for years, decades, perhaps even longer than either of us. Every year, if we tend it properly, it will bloom anew, bringing fresh flowers into our home."
I understand that cut flowers still have their place, and that they have a much bigger immediate impact. I also understand that some people are better able to tend flowers and plants than others. There aren't many plants that can survive being coffeed instead of watered, for example. I just wanted to take a second and share my thoughts on the matter.
Good luck in your quest. Hope I've been of at least some help.
Paul
Jude
(My six year old lovingly made me an arrangement of sponged flowers and a hand written 'For Mom, Love Carter' heart shaped note. 
Jude