Is there a bra that protects your implants from excessive pressure in sports like grappling/BJJ?

It would take an enormous amount of pressure for an implant to rupture - literally tons of pressure would be needed.You’d most likely suffer from a serious injury before your implants rupture. 
For that reason, I recommend just wearing a good sports bra that compresses your breasts sufficiently to “keep them out of the way”.

As far as I know, there is no bra specifically designed for the purpose of protecting implants for high impact activities.  Your best bet use a bra which is very compressive to minimize the ability for an opponent to be able to grab and manipulate either breast.  However, no bra is going to protect you against the possibility of rupture if you were to land on the floor directly on your breast.  Pursuing this kind of high impact sport carries with it at least some degree of risk.Best of luck!
Dr. SubbioBoard-Certified Plastic SurgeonNewtown Square/Philadelphia, PA

Implants are pretty durable. If you want more hold during your exercises, then get a really good sports bra.

Thanks for sharing your question. I can appreciate your concern.

My favorite is the Knockout bra from victoria secrets. it keeps the pocket and prevents migration of the implant laterally.Finally, make sure that you have a consultation with a board certified plastic surgeon.
Wishing you the best in your journey