I'm also a parent of a child adopted internationally. While this may not work for the shower, it is a wonderful gift for the actual adoption date or readoption date. For both the U.S. and the State of TX, you can get a flag that was flown over the national or state capitol on a specific date. It is surprisingly affordable and a cool gift that almost no one even knows of or thinks about. Super easy to order too, just be sure to order it in advance of the actual date needed. Also, you can have your State Senator send a letter of congratulations to the little one just by requesting it from their office (There are forms on their websites to make the request.) For example, Sen John Corryn sent my daughter a letter congratulating her on her adoption and U.S. Citizenship. Also a mainly Texas thing, but one of the best dang gifts that I ever received was a gift certificate to Adventure Kids (Playcare) where I could get out alone for a few hours. You may also want to consider a photo album or frame, and I cherished a baby blanket that was made for her. Other items that are useful for a shower are things to make travel easier (snacks, kid snack bowls, toiletries, etc). Arriving home with a 2 yr old, there were very few "baby" things that I ended up truly needing. The best thing by far was one of those clip on mirrors that attach to the rear view mirror or visor to see her in the back seat where I could see what she was doing and could make eye contact wtih her at stop lights. A diaper bag was also very useful. Other items were a jogging stroller, a wagon, car organizer and baby seat. A ride on toy is a good idea, too. My daughter loved a Fisher Price Horse that was pink and rolls and plays some music...it was about $40 from toys r us and the top end of the age range is 36 months, but she used it longer. A tricycle will also be helpful after a bit. A memorable gift that we will always keep is an incredibly soft baby blanket with an incredibly soft (think "made for infant) stuffed dog, as the softness is very soothing. There's also a children's book called "A Mother for Cukoo" that is a sweet adoption book and not specific to country. You also can find ideas for things from adoptshoppe.com. Also Bronner's specializes in ornaments of all type, and they have Christmas type ones that say "Adopted with Love" and are personalized with the child's name. They also have a lot of ornaments, etc that are flags or landmarks for specific countries. Appropriate for either now or Christmas.
I'm assuming your brother and his wife are in Texas, and our state requires a "readoption" once the child is home. They will have to do this to get the TX birth cerfiticate. So, they will have multiple dates with sentimental significance. Personally, I'm not a fan of the term "gotcha day," and so we celebrate "family day."
Congats to your brother and his wife.