My parents are divorced and my mother took possession of the original copy of my birth certificate. She won't give it back to me because she claims it's "hers". Is there any way to get a copy of the orignal document?

Sure. Just go to the registrars office and ask for a copy. They may charge you for it, but it shouldn't cost much.

My parents are divorced and my mother took possession of the original copy of my birth certificate (The commemorative birth certificate). She won't give it back to me because she claims it's "hers". Is there any way to get another copy of it?

Determine county you were born in call and they can send you a certified copy.

I'm not sure what a commemorative birth certificate is. I suspect it's a fancier copy of the official certificate issued at time of birth. If your local bureau of vital statistics will issue copies of it, you can request one from them.

If you just need a copy of your birth certificate that's where you get one.