Methanotrophs use methane as their sole source of C and energy. They are single biological entity, which can help in the mitigation of most potent GHG in the atmosphere.
it depends a bit on what you want. Do you need any methanotrophic culture? Than you could either buy some from a strain collection or you could ask a collegue to send you some.
Or do you want to isolate MOB from "your" environment? Than you could you use some of the techniques describe above or some simple mineral medium with methane. However from isolation MOB to getting a real pure culture is a long long way....