If there's bradycardia, is there bradypnea for slow respiratory rate?

Yes: The medical definition of bradypnea (or bradypnoea) is abnormally slow breathing rate (respirations per minute) and as in heart rate the number will depend on the patient's age.

Short and Sweet: Yes: Bradypnea is a proper medical term for slow breathing. It is a clinical sign of central respiratory depression due to drug intoxication and brain failure from other causes, but a slow respiratory rate is not necessarily abnormal. In fact, bradypnea at rest is common in healthy folks and trained athletes. Dr. Mike.

Yes: The medical term for an abnormally slow breathing rate is bradypnea although it isn't commonly used in medical practice.