Loads of places.
Have lunch or dinner at Santa Fe, and you may be offered a digestif of Albert's rhum vanille. Thus fortified, make your way to:
First on the list is La Gloriette Boutique, located in the parking lot of the former La Gloriette restaurant. It sells Albert's rum, and if memory serves, nothing but Albert's rum. Posted hours are 10-12 and 2-4, but I didn't ever find it open on my recent visit. Albert's mobile number is taped to the door. Three benefits of shopping here are 1) You get to see Albert, 2) There is more variety, 3) Albert bubblewraps for shipping it home in your suitcase.
Other places where I've seen Alberts rum available are Le Coffee Shop, La Cave du Port Franc, AMC Supermarket, and Petite Deauville. It may be available other places too.
The rum is sold in smaller flasks and larger bottles. The price of the larger bottles was €20 - €23, depending on the shop.