The tequila is then rested in medium-char American oak casks for eleven months and then transferred to hand-selected vintage port casks from the renowned Duoro Valley in Portugal for an additional two months of aging. The double-maturation process accentuates the notes of cooked agave, increases complexity and delivers a nose of dried fruit and ripe plum infused with hints of cinnamon, caramel and chocolate.
When they say "medium-char" I suspect they are referring to medium toast, pretty standard for a wine barrel. You most likely do not want a charred barrel, which in my book is a bourbon barrel, and we are talking black char in this case, with pieces of wood flaking off on the inside. A charred barrel will give wonderful flavors, and I own such a barrel (Woodford Reserve), but I don't think that is what they are actually using.
There are lots of sources for barrels out there, new and used. Used bourbon barrels are relatively inexpensive because they are only used once for bourbon. Wine barrels are also pretty cheap to buy used because there is so much inventory coming out of all the wineries. And, you can even buy a Port barrel, in the United States, that has come from the Douro. These are not so cheap, and I recently passed on one because of the price. Here's a source for used barrels, including Port sometimes:
http://www.rockymountainbarrelcompany.com/ If you really want to get a used barrel of some type, I would contact them. They have connections and inventory coming in all the time that may not be listed on their web site.
One option would be to buy a used wine barrel and then season it with Port. This would give you some nice wine base to then tweak. The difficulty is it will most likely be a large ~60 gallon barrel. Small used barrels can be found, as I own a 15 gallon gin barrel and know a source for 8 and 15 gallon whiskey barrels. But small used barrels in general and small wine barrels specifically are harder to find.
So I'm guessing you're going to buy a new small wine barrel. Those are easy to find in ~5, 10, 20 ... gallon sizes. So what do you do with that? Most importantly, you don't let it dry out. Google for tips on using and maintaining a barrel, as there is good information on a number of web sites, e.g.
http://www.bouchardcooperages.com/usa/c ... intro.html . After receiving the barrel, I would fill it with water and maybe wet the outside as well. (Where do you live? How humid is it?) You want the wood to swell and seal. After confirming that you have a tight barrel, I would drain it out and ideally fill it with Port. But that's a lot of Port. If you can't fill it, I'd put in several gallons (depending on barrel size) and swish it all around. Then I would put the barrel on a stand and let it sit for days, ideally swishing the Port around every day to coat the entire insides, and letting the barrel rest in different positions between swishes. I might put a wet towel on the outside of the barrel depending on how full it is and how humid it is. I have done a procedure like this for barrel I have with bourbon and gin.
What Port? Given the volume needed, I'm thinking most likely a standard tawny is what you want. If the description above mentioned more fruity flavors I might use some ruby, but the barrel they are using was probably a barrel that made tawny, and since you don't have 7 years to let this stuff age, tawny will probably give more of the target flavor.
How long? As long as you can stand it? I'm thinking at least a week, and a month would probably be better. The longer the Port sits in the barrel the better, but you also don't want the barrel to dry out either after that initial swelling.
When you are ready to fill the barrel, drain out the Port, but don't rinse, and don't even try to drain out every last drop. I think your fresh draining and Port residue will help the effort.
Just my thoughts ... fun project
