How to get LCOM(Lack of Cohesion of Methods) metric in SonarQube 4.2?

There's no plugin for this, so if you want it, you'll have to develop it.

In any case, we've deprecated and removed this metric because we found it was difficult to compute it correctly and therefore to use it correctly. Maybe this could give you a hint on whether you should keep on considering it or not...

Since Sonar 4.1 LCOM4 metric has been removed because of too many false positives. See Remove support of LCOM4.