I only have seen postings on social media around competitive rabbit agility. From what I’ve seen, they are always harnessed. If you are looking to enter a specific competition or association that holds these events, contacting them may be the best bet in finding what I assume to be standardized rabbit agility equipment?
As a general note, some rabbits are not agreeable to harnesses, and some environments may not be either. Rabbits who may suddenly jolt due to something they sense, their energy level, and/or something in their environment have a risk of being injured when held on a harness/leash, so if you go to try and acclimate your rabbits to harnesses and it seems like their nature due not suit it safely, I would not force it.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.