The only way you can get higher than NRR 33 is by using ear muffs and ear plugs at the same time, and only then can you achieve an NRR of 34 or greater. An NRR of 34 requires NRR 20 ear muffs worn over NRR 33 ear plugs. You can get to an NRR of 36, but that requires the highest rated muff (NRR 30 or 31) and the highest rated plug (NRR 33) to be worn at the same time.
What about beeswax plugs? We do not recommend them because contrary to some claims, beeswax is not nearly as good a noise insulator as even the cheap foam plugs available at the drug store, and none of the major companies specializing in ear plugs accept the claim of NRR 34 as valid.
Source: Hearing Protection Options from the EAR PLUG SUPERSTORE!