We lucked out and found the authentic ingredients — Gosling's rum and Barritts ginger beer — conveniently stocked together in our local liquor store. But just in case some of you are thinking about Dark and Stormies for the first time this weekend, here's a photo of that retro Barritts can you'll be looking for.
Below, a little more about this beer and a link for ordering... Barritts has been made and bottled in Bermuda by the same family for five generations. Ginger beer originated in England (the company's founder came to Bermuda from England) and initially had alcohol in it. This stuff no longer does.
We've honestly never tasted a ginger beer that wasn't Barritts, but we're big fans. It's sweet but not too sugary and has a definite ginger bite that tickles the back of your throat. It would make a great alternative to root beer in an ice cream float, if you aren't interested in combining it with rum. (We do highly recommend you try, though.)
If you can't find Barritts in a store near you, it's available by the case from Beverages Direct: