How do I get a copy of my parents will?

If there was a will and it was probated, a copy would be on file. Google for where probated wills are filed in your mothers state. However it could be there was no will or no need to probate it if everything that would be included in a will was already in your brothers name. If he was her caretaker/ advocate that could very well be the case.

my brother never let me know she died hes kept everything

The Executor of the Will is supposed to call in all beneficiaries for a reading. If they died without a Will, you need a lawyer to probate the estate.