"Service Ceiling" (not called that)
1) Where to find it? Defined by the "environmental flight envelope" in the manufacturer's publications, e.g. Technical Specification.
2) How is it calculated? As B2N2 says there can be many factors. Climb rate is not a hard limit, that's why you won't find it in the regulations. Airbus talks about 300 ft per min as a reasonable number for flight management system considerations, but that's not a ceiling.