Absolutely agree with what's been said.
Training at home in his safe area with little distraction will help cement the desired behaviors before you need to take him out to a distractive environment.
I have a boy who was very reactive (though not at the level of yours) at the various dog events we attended. To fix this, I would sometimes go to class or a local event with him not to participate but to "acclimate"; we would just site there and watch. At first I would bring his crate along and he would get treats dropped in the crate every time another dog came near, eventually we worked to the point where he could sit on my lap but still get treats when anxiety levels rose. Now he only gets aroused when particular dogs appear and even then he's pretty laid back compared to previously.
The muzzle idea should work but you will have to train him to accept it first at home before you take him out.
It takes time and patience and you can't rush this.