There are a lot of opportunities to do research in gravitational waves!
The LIGO Scientific Collaboration includes over 100 institutions! If you are interested in working on gravitational wave research, a great place to start is looking at the list of LSC institutions, and see if they include a school you’d like to attend or can reach easily.
In addition, some schools offer summer undergraduate research opportunities through the NSF funded REU program. These tend to be GREAT opportunities, with many expenses covered. To find a program, search the NSF database of REU sites. There are lots of ways to search. I found a search for “gravitational” turns up some good options. You could also look for programs in physics or astrophysics.
Good luck!