it is definitely allowed to get married in Muharram, to say that it is not, is the belief of the Shi'ite,
they believe it is a sorrowful month now because Hadrat Hussein was martyred in this month ( May Allah have mercy on him)They believe that to get married in this month will bring an unhappy marriage. Alhamdulillah, we know that this is just superstitious nonsense.
By sunnah belief it is perfectly fine, if you want ill find you an article later