Are you still considering Huckleberry as a name for your next child, Andrea? :)
Whether or not Mark Twain created a unique name out of a slang expression, there is at least one baby name book on the market which "legitimizes" the name for modern-day use -- *The Penguin Classic Baby Name Book: 2,000 Names from the World's Great Literature*, by Grace Hamlin. You'll find an entry in there for "Huckleberry" as a choice for a boy's name.
-- Nanaea