Does anyone know who to strengthen the inner larynx muscles for singing?

In singing, the larynx is used, but it isn't what you should concentrate on strengthening. The larynx is more about placement. You want to make sure you are open, and not tightening up in the area where your larynx is. If you focus on strengthening it visually, I would fear a person would tighten up and not relax, which is counteractive to the sound you want to produce. So instead of focusing on strengthening it, focus on relaxing that area. Not only in your oral and throat area, but everywhere. Yes, singing is about working, but it isn't about working too hard. That is why one should relax, but give more energy as they sing. If you relax, the larynx will fall into place, and your placement will not be as hard to find. Also, we have to be careful about discussing the larynx on this type of forum. Since we all have different anatomies and or bodies are made differently, what may work for you may not work for the next person as to what you SHOULD do in your case. You might have the placement right, and because someone else's experience was harder, might give you advice that in actuality not work in your best interest. This is why it is best to work with a voice teacher so they can see what you are doing right and wrong. A good voice teacher can actually hear and see if your position is wrong or right. But most will concentrate on opening and positioning instead.

What you do want to concentrate on is strengthening your diaphragmatic breathing in your abdominal area. That is where most of your support comes from, and the more you strengthen your breathing in singing (which isn't strenuous at all), the better control you will have over your singing. You will overwork your body less, and you will create more power as needed in your instrument. So if you are trying to improve anything in the "strength" department, work on diaphragmatic breathing everyday. Cardio exercises on machines like the stepper really helps me in that department too. So let the larynx fall as it feels right in your voice. It will improve itself if you develop a good technique, and your body will connect with the voice on its own.

havn't a clue what the inner larynx muscle is, But I heard forcing yourself to yawn and breathing heavily at the same time strengthens something in that general area!

You shouldn't keep the tension up in your larynx muscles for singing. It's more with the diaphragm that helps supports that strength.

Yeah, I heard if you yawn with a sound, it's supposedly good for your voice.