I have a vegan coworker here at Cioccolato, and she does not sit sadly around the shop surrounded by things she cannot enjoy. There are chocolates here that are very distinctly off limits to vegans, like milk chocolate and cream centers, but we also carry some of the world's finest dark chocolate bars, and although not always labeled as such, (because they are imported and European markets are not yet subject to the same strict labeling laws and practices that are in place here in the states) they are entirely suitable for vegans and the lactose intolerant.
The best dark chocolate bars should have a very short ingredients list: cacao mass, sugar, cacao butter, and vanilla. Not all will include vanilla, and many will also include soy lecithin as an emulsifier - this is not necessarily a sign of bad chocolate. In any case, cacao mass and cacao butter come directly from the cacao pod (which is of course the fruit of a plant), sugar cane is a plant, and so are vanilla and soy. No dairy! No animal products whatsoever!
If you are highly sensitive to dairy, you will need to check labels for caveats like "processed on equipment shared by..." and "may contain traces of..." - which warn of the potential of microscopic levels of other ingredients. Producers of fine chocolate will want you to achieve the desired taste they have crafted for you, and will go to lengths to ensure that your chocolate experience is free of unintended flavors or ingredients, even though they may be legally obligated to include such warnings.
Dark chocolate bars of a lesser quality (often cheaper and mass-produced) may contain ingredients unfriendly to vegans and those allergic to dairy, like lactose and even milk fat. You're probably used to checking labels if these issues concern you, but a rule of thumb I would suggest is this: the shorter the ingredients list, the better. Less information to sort out, and greater likelihood of higher quality chocolate. Even flavored dark chocolate bars should only have one or two extra ingredients, like orange bits, coffee, salt, spices, nuts, etc. (all still vegan friendly!)
A good chocolate shop (or website) should be able to provide accurate ingredient information promptly upon request, whether they make their own chocolate or sell someone else's. Don't hesitate to call ahead, ask at the shop, or send an email.

Ultimately it will likely be easier and more cost-effective to seek out a purveyor of fine chocolates than a specialty vegan shop - or if you have both available to you, you simply have more chocolate options. A win-win situation if I ever heard of one!