To clarify, do you mean a newly-discovered species, or a new hybrid?

If it's the latter, do a search for "International Orchid Registrar," as you'll find the necessary instructions and application form there.

As far as I know, there is no "registration" of species. Instead, one must be the first to technically describe the plant and flower in a respected botanical journal, so that it may be peer reviewed. If the taxonomists of the world don't immediately find a flaw in the novelty of the plant, you're good to go.