We need help look for a specialist for my stepson?

His father and I are concerned that he is 3 1/2 years old and he is not talking. He grunts and points to things but that's it. He seems like understands like if we say bike he does the hand motion for a wheel turning. My husband has question his sons mom and she says he is fine. When my husband asked her to make an appointment with the child's doctor to see if he could refer him to some specialist she said no. So now my husband wants to look for one but don't know where to start.? Is there a speech therapists for young children???