Oh man, what a time to get into alpine snowboards! There's been so much progression in the last few years, which is continuing now. Fifteen to twenty years ago, about 25% of the riders at my local east coast hill were on alpine setups. That percentage faded as terrain parks became the rage. I've seen a resurgence in alpine gear in the last few years as newer designs and materials have come into play. No longer are high performance carving setups limited to super stiff, unforgiving boards. Now, hardboot specific gear can be found tailored from full race, to recreational carving, to all mountain use, and even powder. Boots and bindings as well have advanced and can be found (or adjusted) moderately soft to very stiff. Overall of course, their main intent is to tear up groom in thigh scraping carves, but forgiveness, flexibility, aggressiveness, and intended speed are now viable considerations. The three manufacturers that you mentioned are highly respected. I own a 182 Coiler NSR2 with the titanal construction and love it. In fact, I've sold off everything else except my vintage softie setup that I reserve for sled hill outings with my kids. (Check out Coiler's website, recently updated. Everything is custom order.)
When you first get on an alpine board, it will probably feel awkward at first if you're used to a softie setup. But you'll get the feel for it. Once you start pushing carving carves harder and harder, you're going to be shocked at how well the edge holds and left wondering how on earth it's even possible to be doing what you're doing...which IMO is also why you'll want to buy a board that suits what you "intend" to do instead of what you think your entry level skill is "now". Also, be aware that hard top to bottom carving in hardboot gear is much more physically demanding than loose carving or skidding turns with soft setups. Pulling high G's is the name of the game and screaming thighs come par for the course as you work up to it.
Unfortuantely, with few exceptions, you're not going to walk into a snowboard shop and find alpine gear. You're probably going to find you'll have to buy all your alpine gear online. As already mentioned, Bomber online is a fantastic resource for information and gear in the classifieds. Especially with more modern gear coming into use, slightly older (especially glass construction) boards can be found for a song if budget is a constraint. Bomber, though, just like every message board I've visited, has its share of jackholes vs. insightful enthusiasts and of course contradictory opinions, so you'll have to sift through the wheat and chaff. Read up, read up! Seek out a hard boot instructor if you can. I've been fortunate to have spent a couple of training sessions with Olympic level coaches and take their word for gospel. Enjoy!
Incidentally, just to make corrections and / or add to some of the above posts, a "monoski" is a ski (not a snowboard) where the feet are locked side by side, as in permanent parallel skiing. "Alpine" snowboards refer to hardboot snowboard setups generally aimed at high performance carving. "Skwal" boards are uber-narrow snowboards where the binding angles are at or approaching 90 degrees...a real fringe sport!