Without knowing exactly what these people like, one guideline is to look for beer that’s bottled individually. It might be hard to go out looking for specific beers, so I’ll just give you guidelines. Depending on the alcohol laws where you live, you might be able to find beer in a gourmet grocery store, a big store like total wine and liquor, or just the liquor store, or a wine shop. (Stores that focus on wine will often have a selection of gourmet beers, too.) Beers that are sold by the individual bottle are usually either really high-end or really low-end, because they’re going for two different markets. They’re outlawing individual beer sales in some places because a lot of the time homeless people will just buy them and drink them on the street. At the other end of the spectrum, some beers are meant to be enjoyed more like wine, and they’re sold in bottles that are maybe around 20 ounces to a liter. These usually cost anywhere from a few dollars to maybe ten dollars. A good example is Chimay, which I think is pretty much always sold this way. (How much do you want to spend on their gift?) The good thing about doing this is they might open it then and share it with you. :)
Where ever you go, talk to the salespeople and ask them what the beer is like or for recommendations. They’ll probably be more helpful if you go to a specialty place. Not everyone likes Yelp, but I think it is great for retail. It might be cool if you got these guys a Trappist beer. The name means beers that are brewed by Trappist monks, mostly located in or around Belgium and the Netherlands. They have a broad range of styles, but are known for quality, and this might be the unique sort of thing you’re looking for.
This is a very daunting beer menu of a pub in my area. It would take forever to try everything on that list, and anyway they’re usually out of half of it at any one time. But it at least might help you to know the names of a bunch of alternative breweries out there. Anyway, it might not matter too much what you get them. I always appreciate free beer.